This movement is in all early mens size Heuer diver, both 38mm and 42mm.

After some time the "L" version appeared. All "L" Heuer/Tag Heuer divers I have seen/handled have a different ESA early quartz movment. It's easy to spot with it's battery placed upside down. These "L" watches is easy to date. The year is printed on the movement. I can find the ESA number for this movement later today. I have to open a watch to look.

Movement in a "L" diver. This movement is a little lower than the first ESA 536.121 so the case had to be a little modified. Dated from 1985.

Finally in the "N" the movement is the ETA 955.114. This is a musch slimmer movement so the case is modified again. The case back is often lower than in the earlier watches.

ETA 955.114 as in all "N" divers. Easy to date, this one has 90 (1990) stamped on the movement.

This is what I have concluded after I have studied a lot of pictures and handled some of these watches. I might be wrong but I think this is the answer.

If you could open your 980.023L and see if it has the movement shown in the middle, with the upside down battery, we have a conclusion.

Regards
Jarl
www.classicheuers.blogspot.com