"Why is it OK in one instance to sign for an incorrect score and not in another?"
/Alistair Tait reminds us of one other "inconsistency" in the rules of golf that he believes should be remedied after the latest DQ for signing an incorrect card, even though the player did not know it was an incorrect card at the time, nor did his playing partner know that. Because it wasn't!
If you sign for a 6 instead of a 5, then under Rule 6-6d you are allowed to continue in the tournament. Yet sign for a score lower than you actually take and you’re disqualified.
Let’s be grown up about this. There would have been no harm in Villegas continuing in the tournament, but with a two-stroke disadvantage. The R&A and USGA should get their heads together to implement this policy.