Heuer used to serialise the movements but that practice ended in the 60s when they took to serialising the cases instead. A few years later the model reference was also added.

Those were both between the lugs, in slightly different positions depending on the model. Late in the '70s they changed their minds again and put both references on the caseback. Always thought that a strange decision, a simple caseback change meant the watch lost its original identity, and the numbers were exposed to much more wear.

Good that yours are still visible. We don't see many Veronas - I think the grey is particularly handsome but the black is nice too!