When the counterfeit PCGS holders were discovered, there were several reactions. Up until then the technology (slab) was assumed to be sufficient proof of authenticity.
PCGS changed the label to a more secure one (the microprinted dots that make up the doily were of a size and in a color that photocopies of the day couldn't image). And the 3rd piece (ring) was added to prevent the slab from being pried open (although I've seen no proof that it could have been).
But those were interim measures until the two piece slab became available, so the doily in a three piece holder was a short term item. Surrounded by the far more common rattlers and common green label 2 and 3 piece holders.
FYI- the post-doily green label was equally hard to photocopy.
-----Burton
50+ year / Life / Emeritus
ANA member (joined 12/1/1973)
Life member: Numismatics International, CONECA
Member: TNA, FtWCC, NETCC, EveryCountry (online) coin club
Owned by three cats and a wife of 40+ years (joined 1983)
Author: 3rd Edition of the Sample Slabs book,
https://www.sampleslabs.info/