With every Smash update, every recordings are completely usable.
(OOR: Out of Rant)
Well how is that? Well the in-game saved matches actually saves the controller inputs and other mechanics into a short memory box for when the player decides to save or not. So, with every update, character balances are made, and so if you were to recreate the same button input, some changes can be noticable, and therefore may desync with the original match. Example since Ganondorf now has super armor on his turn-around warlock punch, he can't flinch. Prior updates did not have it, so you hit him, he gets knocked back. However using the same saved match (saved controller input match) the outcome will be different and therefore will not yield the same result. It is why every update makes past saved matches obsolete.
---To the Rant----->
Why am I annoyed of this? Well... I don't own a Wii U unfortunately. However I have a nephew who does and we have lots of fun and record good matches. He doesn't come very often and when he does, I use my capture card to forever save the moments.
There are times the update has to be made, and the saved matches become obsolete, and therefore have no choice but to delete the matches. Gets me annoyed cause I didn't get the chance to actually record them before the updates roll out, and some of them were good ones.
Well... wasn't that bad to have an update roll out after 2-3 months (unlike the other update that broke Diddy once again and had to roll another update in 3 days or he be broken OP again. Had a good saved match in that time too.) At least now they have updated to render and upload straight to Youtube. Though I like the quality the Elgato capture card delivers much better. (Hehe Elgato. It is like saying spanish for Thecat)