I can only say for sure that it changed between 2337A and 2419A!
But I can not narrow it further down.
My investigations so far are like this:
LCDType Bat.contact PCB confirmed Ser-Nr
LCDsepBoard tin/silver two separate 2326A,2337A
LCDfullMuPx spring/gold onePCB 2419A,2438A,2439A,2509A,2521A,2538A,2623B,2626A
LCDhalfMuPx spring/gold onePCB 3437S,3521S
The LCD changed to half as much Multiplex (MuPx) connections somewhere after 2626A and before 3437S.
These numbers are from my samples (which I can verify).
Most probably it depends on the manufacturing location and isn't consistent for different locations.
Hope that this fragment adds to the truth out there ;-)
Thank You!
Well the HP-10C that I just bought is 2305A, so my guess is it is 2 pc (have not received yet). That's good as it has a dent in the bezel. Hopefully I can straighten out easier than the 2 pc design.
Edited: 5 May 2011, 10:18 p.m.
I doubt you can narrow it any further as it varies among the the different models. The overall range for the family is somewhere between 3rd Q 83 to 2nd Q 84 which is reflected in exschr's data.
FWIW, I have never seen a one board 10C and I do not believe they where ever built. Supporting this theory is the museum listed Introduction-Discontinuation of 1982-1984. So, it would stand to reason it was discontinued during the design change-over to the single board.