user8305: In Buddhism we classically have four stages of enlightenment:

Stream-enterer (Sotapanna);
Once-returner (Sakadagami);
Non-returner (Anāgāmi);
Arahant.

My question, as stated in the title, is: can a person attain to any one of the four stages mentioned above without clearly recognizing it?

user-1: Ransara,
Yes, in regard of the question, it's possible that one is not aware of certain paths and fruits. As for the Arahat, my person is not sure about it, but one could investigate some situations in the Suttas. 
Many do not know their current wealth, but that is mostly good, since it caused suffering thinking "I am this or that", not to speak of questioning "Am I this or that.
So when asking your self or other, simple ask if this or that work has been already done. So if not "the task is done, there is no more further for this world (or a next)" arsises, is know simple: Work, and take on all possible given possibilities for it.
One having done
Not easy to do
Should not be scared 
To delight in it
Nor should one
Reject done merits.
For it is hard
To gain such a life
And its even harder
To gain such again:
Meeting either
The good Dhamma
Or upright leading man.
What ever good
Has been done
Achived, sacrified,
Only those delighting,
In deeds hard to do,
Having gratitude,
Form themselves and
In regard of others
Their sacrifies, their deeds,
Are able to carry themseves
Beyound.
Anumodan(e)a!
(Note: this answer is a gift of Dhamma and not meant for any commercial purpose or other worldily gains.)

user10293: Especially the stream-enterer in some cases if not fully guided by the meditation master will not be identify clearly which stage he/she achieve. Only with the help of the meditation master who can teach how magga and phala was achieved during practice will know exactly what is what. Once in Buddha time, one upathaka didn't know his afterlife whether might be in lower realm although he already entered sotapanna stage which I heard from one of my venerable sayadaw highlighting the importance of meditation master. 

user362: 
Samyutta Nikaya - Maha Vaggo (2) Sotapatti Samyuttaya 

Here you can find sutta where Buddha explains who a Sotapatti stream winner is. 

Unwavering impression of Buddha 
Unwavering impression of Dhamma 
Unwavering impression of Sangha 
Maintains Aryakäntha sîla 

There are other places in Tipitaka where Buddha mentions the first three and the fourth one as 

No doubt of The Four Noble Truths (Sammä Ditti) - 

A definitive answer may be found here: 

Samyutta Nikaya - Maha Vaggo (2) Sotapatti Samyuttaya - 11.1.5

As you might notice, as long as there is doubt (Vicikiccä) you are not sothäpanna. By observing your own mind, you can confirm if you are sothäpanna or not. 
To go a step further, it is wise to practice Buddhism with the thoughts 

As long as I make assumptions using "me", "mine", "my soul" I need to practice detachment. 
As long as I have craving, anger or delusion, I will practice detachment, metta and vipassana (Sammä Ditti) 

This way, one won't waste time thinking am I this, am I that. Where there is craving, anger, delusion, there is harm for oneself and others. Therefore, you can practice this just by deciding to be harmless. 

 English Version

8305: <p>In Buddhism we classically have <a href="https://en.wikipedia.org/wiki/Four_stages_of_enlightenment" rel="noreferrer">four stages of enlightenment</a>:</p>

<ol>
<li>Stream-enterer (Sotapanna);</li>
<li>Once-returner (Sakadagami);</li>
<li>Non-returner (Anāgāmi);</li>
<li>Arahant.</li>
</ol>

<p>My question, as stated in the title, is: can a person attain to any one of the four stages mentioned above without clearly recognizing it?</p>
 -1: <p>Ransara,</p>

<p>Yes, in regard of the question, it's possible that one is not aware of certain paths and fruits. As for the Arahat, my person is not sure about it, but one could investigate some situations in the Suttas. </p>

<p>Many do not know their current wealth, but that is mostly good, since it caused suffering thinking "I am this or that", not to speak of questioning "Am I this or that.
So when asking your self or other, simple ask if this or that work has been already done. So if not "the task is done, there is no more further for this world (or a next)" arsises, is know simple: Work, and take on all possible given possibilities for it.</p>

<p>One having done</p>

<p>Not easy to do</p>

<p>Should not be scared </p>

<p>To delight in it</p>

<p>Nor should one</p>

<p>Reject done merits.</p>

<p>For it is hard</p>

<p>To gain such a life</p>

<p>And its even harder</p>

<p>To gain such again:</p>

<p>Meeting either</p>

<p>The good Dhamma</p>

<p>Or upright leading man.</p>

<p>What ever good</p>

<p>Has been done</p>

<p>Achived, sacrified,</p>

<p>Only those delighting,</p>

<p>In deeds hard to do,</p>

<p>Having gratitude,</p>

<p>Form themselves and</p>

<p>In regard of others</p>

<p>Their sacrifies, their deeds,</p>

<p>Are able to carry themseves</p>

<p>Beyound.</p>

<p><em>Anumodan(e)a!</em></p>

<p><em>(Note: this answer is a gift of Dhamma and not meant for any commercial purpose or other worldily gains.)</em></p>
 10293: <p>Especially the stream-enterer in some cases if not fully guided by the meditation master will not be identify clearly which stage he/she achieve. Only with the help of the meditation master who can teach how magga and phala was achieved during practice will know exactly what is what. Once in Buddha time, one upathaka didn't know his afterlife whether might be in lower realm although he already entered sotapanna stage which I heard from one of my venerable sayadaw highlighting the importance of meditation master. </p>
 362: <blockquote>
  <p>Samyutta Nikaya - Maha Vaggo (2) Sotapatti Samyuttaya </p>
</blockquote>

<p>Here you can find sutta where Buddha explains who a Sotapatti stream winner is. </p>

<ol>
<li>Unwavering impression of Buddha </li>
<li>Unwavering impression of Dhamma </li>
<li>Unwavering impression of Sangha </li>
<li>Maintains Aryakäntha sîla </li>
</ol>

<p>There are other places in Tipitaka where Buddha mentions the first three and the fourth one as </p>

<ol start="4">
<li>No doubt of The Four Noble Truths (Sammä Ditti) - </li>
</ol>

<p>A definitive answer may be found here: </p>

<blockquote>
  <p>Samyutta Nikaya - Maha Vaggo (2) Sotapatti Samyuttaya - 11.1.5</p>
</blockquote>

<p>As you might notice, as long as there is doubt (Vicikiccä) you are not sothäpanna. By observing your own mind, you can confirm if you are sothäpanna or not. </p>

<p>To go a step further, it is wise to practice Buddhism with the thoughts </p>

<ol>
<li>As long as I make assumptions using "me", "mine", "my soul" I need to practice detachment. </li>
<li>As long as I have craving, anger or delusion, I will practice detachment, metta and vipassana (Sammä Ditti) </li>
</ol>

<p>This way, one won't waste time thinking am I this, am I that. Where there is craving, anger, delusion, there is harm for oneself and others. Therefore, you can practice this just by deciding to be harmless. </p>

<p><a href="https://i.stack.imgur.com/NVE7J.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NVE7J.jpg" alt="Sinhala Version"></a></p>

<p><a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/16.5-Sotapatti-Sariputta-S-2-s55.5-piya.pdf" rel="nofollow noreferrer"> English Version</a></p>
