Apparently the first batch of 127s released were met with criticism about the distortion as well as other criticisms so OP changed that for the next batch in doing so the AR was slightly less but still purply blue, then the batch after that had a slightly different thickness at the edges as their were still comments. I think what happened was OP tried a few different techniques to reduce it but they did maintain the shape on top.
There then followed the OPCS versions, ie the replacements that were made once the original and last batch run out, apparently though you can still be given the very first ones if you send it in..!
When the 217 came out OP took note of the 127 issues and basically and as I understand there were 2 runs plus the replacement stock run each had minor variations mainly in AR & Thickness.
The easiest way to tell a gen 127 to gen 217 is at the base edge, the 127 even the later version crystal is thicker than the 217 and a slightly different finish. The finish created by the grinding rubbing process. Also the 217 had a clear/Grey AR whereas the 127 always had a purply blue but to varying strengths not sure about the replacements though...
The crystals I have had certainly support this but its only from research and getting second hand info from ex OP employees, Risti etc that i say this so I wouldnt say that is written in stone....Just what I have picked up and seen for myself...