Collecting vintage Heuer Autavias is a very interesting topic. Some of them were made for military use (Argentina Air Force), there are "Skipper" versions, there are "Mareographe" versions, there are the GMT versions and there are the plain 2446 (three subdials) and 3646 (two subdial) versions.
Heuer produced the first badge of GMT's in 1968. The so called "first execution" has only been in production for a very short time. The most distinct feature of those "1st execution" is the thin Pepsi bezel. Depending on literature, it seems to be confirmed that probably only some 200 or so of these "1st execution" have been produced and it seems that only a handful have surfaced to be still existing.
The very interresting thing about my "1st execution GMT" is the absence of "Swiss" and the absence of "T" on the 6 o'clock sub-dial. This is so far the only GMT that has surfaced with "Swiss" and "T" missing. In addition, all those few "1st execution" that have surfaced so far have case numbers 100xxx. This particular example has a case number 95xxx.
It is therefore most probably the earliest known Heuer Autavia GMT and the absence of "Swiss" and "T" might even indicate that it has been a sort of pre-production prototype or test version.