From your letter versions?
 

I was listening to the From Your Letter song from A Song For XX, and someone sent me recently remix one from sleeperspaceborn.

When I was listening to both, I realized vocals are very different in many places, and I was wondering how sleeperspaceborn got such a version for his remix??? Did the vocal track of From Your Letter sound different from the actual song???

i never heard the remix so can't really tell...
but maybe Ayu re-sung it for the mix??

the remix is a fanremix, so no, Ayu didn't re-sing it... The author of the mix played with Ayu's vocals, and changed them digitally.. Ended up being really nice.