I now have two of these titanium 225.206 chronographs as well--and both have the same serial number: 122053. I purchased one new from a Washington D.C. dealer on 11 August 1986 and the second via eBay last week (it has yet to arrive). It's possible I have purchased the same watch the collector had in 2014. It seems to me that unless this duplication of serial numbers was a known phenomenon during the chaotic last days of the Heuer family ownership, due either to distracted or sloppy manufacturing (or malfunctioning stamping/engraving machines), the likelihood of one being a real Heuer and the other a fake has to be considered. More investigation will be done with my watches and if anything surfaces to suggest the creation of a fake, I'll post the results.

 

Makes sense; checking movements and inside casebacks is next step.

 

If I remember correctly, the first digit of this model identifies the automatic or quartz movement; but I think you’re right about the significance of the numbering overall. What we need is someone from the manufacturing side of the company to weigh in on the history of these titanium watches.

 

Actually, we seem to be confronted here with three of these “122053” serial-number 225.206 watches, not two. If they’re all genuine, surely a quality-control manufacturing problem is behind the situation. Reminds me of the mis-minted coins and mis-printed stamps so highly valued by the numismatics and philatelists, though it’s hard to see how anyone but those of us who have owned and used Heuers would care very much. Somewhere in the TAG Heuer files lies our answer but we won’t know it until someone does the tedious research there what the real answer is. Meanwhile, the best we can do is shrug and say something like, “Hmmm....”

 

I'm quite glad this subject has been reopened-I saw it some time ago and always like to make sense of things. My initial thought was similar to dc's first idea-it is a case or movement code, for example.

I can say there are a large number of examples all with the 122053 code, not just a few so maybe we do need to look closer at comparing the features of these, including the internals as you say.....

 

In support of the case-ID suggestion, I note that the 122053 models have case-back cutaways for the pushers, as does the -054 item, whereas the 122117 does not. A running change in case manufacturing, perhaps.

 

Evidence for the "122053" being a case design ref. number; I just found a couple of automatic 125.206 titanium chronos with the subsidiary number "122117"--the same as the quartz version noted above. This can't be due to counterfeiting or manufacturing errors, but surely reflects, as suggested by several, that the 122053/-054/-117/-417 numbers refer to case or other non-movement-related changes as the watches were developed. Here is one website, for example, advertising a 125.206 with a 122117 case number--and the case back looks identical to the quartz version, Just an idea.
https://www.watchuseek.com/threads/...omatic-lemania-mint-condition-reduced.746409/