Is this proof reasonable, given this information? Suppose I have the figure in the image marked 'Original':

Visually, that figure appears to be a parallelogram.
Would the following proof that $\bigtriangleup BCA \cong \bigtriangleup DAC$ be valid?


*

*$BC \parallel AD$, because Diagram

*$\angle BAC \cong \angle DCA$, because Alternate Interior Angles

*$AC \cong AC$, because Reflexive Property of Congruence

*$AB \cong CD$, because Diagram

*$\bigtriangleup BCA \cong \bigtriangleup DAC$, because Side-Angle-Side congruence postulate


I ask because the figure marked 'Alternate' has the same markings ($AB \cong CD$, $BC \parallel AD$), but side CD is in a different position and side AD is longer, so the two triangles are not congruent.  So I'm not sure whether you can say that the original figure is in fact a parallelogram, just based on the information shown, which must be true for step 2 in the proof to be valid.

Your step (5) says it's using side-angle-side, but the pictures show the configuration is side-side-angle, which does not imply congruence precisely because of this kind of counterxample.
