....the meaning in terms of mintage as the 76-200 (R4) might not apply in this case.
The rarity scale
you reference, was originally developed by Dr. William Sheldon from his
study of early US Large Cents.
The "76-200" figure was not meant to portray the original mintage
of a given coin (or specifically in Sheldon's case, a given die variety of large cent), but rather the estimated/known surviving population
of a specific coin or variety.
The Sheldon scale
is essentially as follows:
R-1 Common (> 1,250 known)
R-2 Not So Common (501 - 1,250)
(201 - 500)
R-4 Very Scarce
(population est at 76-200)
R-6 Very Rare
R-7 Extremely rare
R-8 Unique or Nearly So (1,2 or 3)
I believe there are other rarity scales
developed more specifically for ancients (e.g., R, RR, RRR, etc..). But personally I am not that familiar with them.