user1525: I believe my two title questions are the same (are they?):
Heretofore, what is the longest chain of orphan blocks (of N blocks), such that if someone didn't wait for N+1 confirmations, they may have assumed transactions to be completed when they were not.
For example, on the wiki's blockchain article, it shows orphan chains of two blocks (N=2). In this case, 3 confirmations would have sufficed to confirm transaction with absolute accuracy. https://en.bitcoin.it/wiki/File:Blockchain.png
I ask because it seems 120 confirmations is the gold standard, if you will, as generated bitcoins take that long to confirm. Most other transactions are considered irrevocable at 6 blocks, but what has been the minimum, thus far? 
PS. Is this question even answerable!?

user53: Yes, the question is answerable, although it might be hard to get the data to answer it (you would need blockchains from a few very long-running, well-connected nodes that contained both the main chain and orphan chains).
I don't know the answer. As ThePiachu says, the longest orphan chain was 53 blocks, but I don't think any confirmed-on-one-chain transactions ended up unconfirmed on the other chain-- I don't think there were any double-spends across those two chains.

user323: The longest orphaned fork was created due the "value overflow" bug occurrence, ranging from block 74638 to 74691 (so 53 blocks). Such a situation is unlikely to ever repeat though.
Other than that, as far as I remember 4 blocks were overwritten by some strange behaving miner (related question), but I might be mistaken.
In general, 6 confirmations is enough in most cases to prevent any double-spend attempts, and 120 confirmations is enough to give the developers time to release a fix for some major bug that might occur before the coin creation transactions are mixed in with everything else, creating a big mess.

1525: <p>I believe my two title questions are the same (are they?):</p>

<p>Heretofore, what is the longest chain of orphan blocks (of N blocks), such that if someone didn't wait for N+1 confirmations, they may have assumed transactions to be completed when they were not.</p>

<p>For example, on the wiki's blockchain article, it shows orphan chains of two blocks (N=2). In this case, 3 confirmations would have sufficed to confirm transaction with absolute accuracy. <a href="https://en.bitcoin.it/wiki/File:Blockchain.png">https://en.bitcoin.it/wiki/File:Blockchain.png</a></p>

<p>I ask because it seems 120 confirmations is the gold standard, if you will, as generated bitcoins take that long to confirm. Most other transactions are considered irrevocable at 6 blocks, but what has been the minimum, thus far? </p>

<p>PS. Is this question even answerable!?</p>
 53: <p>Yes, the question is answerable, although it might be hard to get the data to answer it (you would need blockchains from a few very long-running, well-connected nodes that contained both the main chain and orphan chains).</p>

<p>I don't know the answer. As ThePiachu says, the longest orphan chain was 53 blocks, but I don't think any confirmed-on-one-chain transactions ended up unconfirmed on the other chain-- I don't think there were any double-spends across those two chains.</p>
 323: <p>The longest orphaned fork was created due the <a href="https://en.bitcoin.it/wiki/Common_Vulnerabilities_and_Exposures#CVE-2010-5139" rel="nofollow noreferrer">"value overflow" bug</a> occurrence, ranging from block 74638 to 74691 (so 53 blocks). Such a situation is unlikely to ever repeat though.</p>

<p>Other than that, as far as I remember 4 blocks were overwritten by some strange behaving miner (<a href="https://bitcoin.stackexchange.com/questions/3332/what-can-be-done-about-the-no-transaction-block-relayer-currently-71-123-170-15">related question</a>), but I might be mistaken.</p>

<p>In general, 6 confirmations is enough in most cases to prevent any double-spend attempts, and 120 confirmations is enough to give the developers time to release a fix for some major bug that might occur before the coin creation transactions are mixed in with everything else, creating a big mess.</p>
