How previous of threads? This past match was the first time the "all-in" rule was in effect--if a residncy program wants to offer any positions in the match, all their positions must be in the match.
Prior to this year, prematch offers were perfectly kosher per NRMP rules.
supposedly, there should not be any more pre-match offers from this year forward. Makes me wonder what will happen to all those in research fellowships not having a guarantee.