recomputing lenses from batch to batch???

[Ichiro Suzuki <suzuki@blatz.cs.uwm.edu>]

I read an article that states that "until recently" each time
a piece of glass was produced for a particular lens, 
the lens manufacturer measured its actual refractive index and
recomputed the optical design slightly to maintain the original target 
performance, and this contributed to the slight differences in 
performance of different batches of the same lens.
I read another 1953 article in which a Nikon engineer says the same
thing.  So perhaps it was true before the days of platinum crucibles,
but I found it interesting.  Has anyone heard of this? --Ichiro