[Misunderestimated]

I've never been entirely clear about where the line is between legitimate variations (which are a big deal for hardcore set collectors like me) and stray printing errors (which are kinda interesting but that's about it)*....
Of course once any error gets catalogued as a legitimate "variation" all bets are off and -- Presto! -- its a big deal to set collectors, like it or not... **

I guess the classic variation is one where there are simply two versions of something (the T205 Eddie Collins and Roger Bresnahan cards), or the manufacturer corrects or changes something -- the team name because of: a trade (T202 Devlin or T206 Dahlen); a failed team relocation (74 McCovey); a retouch to obscure an obscenity (89 Fleer Billy Ripken) or some other error (89 UD Dale Murphy Rev Neg).

For instance in the T205 set:
The three different Wallace and Chase cards fall on the variations side, along with Harmon and Gray cards
The more recent T205 "discoveries" -- Mathewson (l loss --Cycle) and especially Kaiser Wilhelm ("Suffered") seem to more like printing errors (they ran out of ink or something on some of the cards maybe)

For me, this one (Archer) seems to come down pretty clearly on the printing error side.(Sorry)
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Notes:
*The Frank Thomas Topps RC has the "No Name on Front" printing error that commands big $$ -- I'm not sure what set collectors make of it -- I'm not really sure what a 1990 Topps set collector really thinks like... just buy the whole thing and be done with it?? It is listed as an option on the PSA Registry but no one is over 10% completion (think of the grading costs for 792 cards that are mostly worth nothing and one very pricey "No Name on Front" version!)
** Just imagine how much money would change hands if you could somehow have 15-20 nice, hard to find, specimens of a card that suddenly became a recognized "Variation" in one of the more popular pricey sets -- T206s, 33 Goudeys, 52 Topps etc.... Of course many people thought of this.