Depends on the set, or the type of alteration. PSA is well known for rejecting cards for minsiz or sheet cut (when they detect it) or stored for years in a screwdown holder (shows signs of pressing at the corners which can also hide spooned out creases). Those same cards will regularly get number grades from Beckett and SGC.
The Buster guy has regularly complained about crossing SGC 88 (NM-MT 8) cards to PSA and how few actually cross.
But then there are thousands of trimmed cards that have cleared PSA and they regularly miss writing, added coloring, or erasures on cards which should be seen and given either MK or Altered designations instead of straight/unqualified numbers. Look at the most recent PSA 9 1969 Roberto Clemente's right edge:
https://www.blowoutforums.com/showpo...&postcount=835 How did that card get into a PSA 9 holder honestly?