HP-35 Serial Number Question

[Didier Lachieze]

All production changes didn't drive a date code change (for example with the removal of the famous red dot the date code remained 1143A), so there is generally not a direct link between a specific date code range and specific features sought after by collectors.

You're right in saying that the raised 5 key has historic value as it is present only on the early HP-35 units, this removal happened in January 1973 around the SN 1249A10000 and was not a sharp transition as there is a mix of units with and without raised 5 key between 1249A10000 and 1249A11500. This means that all 1143A, 1230A and most of 1249A plus part of 1143S were produced with the raised 5 key which represents roughly 80k units or ~23% of all HP-35 units.