Not sent in a bunch myself but my favs are my UF4, bought off the shelf on release and removed from the poly about a year ago. Subbed it with the thoughts it was at best a 9.0. Pressed it of course. Came back a 9.8!
And my 2nd fav is a newstand ASM 252, bought it from a shop years ago for $25. Figured at best an 8.0, pressed it also. Came back a 9.4.
And my favorite. Infinity Gauntlet #1, bought off the shelf from a shop as a kid, while my dad was next door trying to sell to the pizza place. Had it signed by Rubinstein last year at Fan Expo, came back a 9.8. Sent it in for Perez signing this year, you guessed it, pressed again. Came back again a 9.8!