Here's one that's stumping me. Some R62A rollsigns have slightly smaller numbers in the bullets, and I assume those rollsigns are the originals and all others are replacements, but I'm not sure.
Here is a 1995 David Pirmann photo of an R62A 
with the small number bullet:
Here is a 2014 Denilson Gomez photo of an R62A with the larger number bullet. This looks more like what you see on the daily:
But here's a 1996 Eric Oszutowicz photo of an R62A with the larger number. Is it possible that between 1993-1996 the rollsigns were replaced, and this photo shows one of the new signs, or were there always a couple sets of signs? [For those keeping score, 1811 wears a sign with the smaller number.]
The distinction that seems pretty clear in age is the "Local" and "Express" lettering beneath some signs. Given that this writing is written in Helvetica, which would not have been the font of choice upon delivery from 1984-1987, I think this must be a sign of a newer rollsign.
This undated but likely late 1980s (the rubber gasket still lines the RFW) Daivd Pirmann photo shows the diamond sign with no lettering, and I assume this is the early sign. [1966 still wears this diamond-6 bullet with no lettering underneath, for those again keeping score.]
Just for confusion, this 1993 Mark Feinman photo shows the 'Express' lettering under the diamond. So maybe the change happened earlier than 1993?
My best guess at this point is that in the early- and mid-1990s most R62As received new rollsigns with new "Express" lettering beneath the 
and 
rollsigns. These signs would have larger numbers on bullets, as is consistent with the MTA's general increasing of lettering size on rollsigns for R46s, R68/As, and others. I should note that there is definite proof of a new set of R62A signs from the few sets on the Shuttle that have a Helvetica-variant 
rather than an Akzidenz-Grotesk . But that may be an even more recent change. A few sets like 1811-1815 and 1966-1970 then kept these older signs, and those are responsible for the confusion we have now. Of course, the real way to check is if anybody has access the end script of an R62A rollsign, where the date is printed...