So if I understand correctly, Heuer started with some number (1, 100, 1000) on the first watch and then they have continued with numbers. And in the company (I assume) there was one machine to print the number and worker had for ex 500 cases of Carrera to marked this way (for ex. 96743 to 97243) then 300 cases Autavia (97244 to 97544) etc.?

If this was like that, then there is a possibility to create some register of serial number / year.

: the case serial number tell us exactly the date when the watch case
: was made, but some watches were assembled later in older cases,
: special in 1946 after the world war they had produced to much
: cases, same happend at Breitling. So Heuer assembled later
: watches in much older cases. For example the first Autavias used
: cases from old tri-compax watches of the 1940th, only made a new
: dial and new becel and ready was the new Autavia from old cases.
: That is also the reason why their exist no Autavia between
: serial number 59+++ and 81+++, the old cases from the 1940th
: were used for the 1. and 2. edition Autavia, the case for the 3.
: edition was made new in 1964.