To be honest, I'm not sure how much this question makes sense.
Multipliers are used for two general reasons:
1) To raise value above the base-set price for shorter-run parallel sets.
2) To raise value for exceptional "swatches" above that of a plain swatch.
Both of these require an "upgrade" to a basic concept -- say, a base set upgraded to a #/50 parallel, or a white swatch upgraded to a 3-color patch.
As such, a multiplier really wouldn't apply to sticker/hard-signed autos, since specific autographed cards are almost never available in BOTH forms. (An exception would be the UD Ice Glacial Graphs, but that is a very isolated incident). Using a multiplier in this way would imply that the "base" version is a sticker auto, but a more-desirable hard-signed version was also available.
As for older hard-signed sets gaining in value -- even if there was evidence to support this on a large scale (which there isn't), multipliers again would be irrelevant. Beckett would simply bump the prices up in the set.
