"On the otherside the pushers are visible on
both sides, which points to a later model
manufactured by Schmitz."

from what i understand
(based on the open front and back pushers case)...i would say for sure that yours wasn't produced in 1972. that much i think i can say accurately. as to locking down the exact year...there i can't help you, sorry.

"This would mean the
the strap does not belong to the watch??"

i don't know if there is anyway to determine that for sure?? from what i could gather from your pic in the first post....it looks like it's the right type.......and, to me, what's important is that it's the correct style for that model. i wouldn't worry so much about trying to determine if it belongs to that exact watch or not.

"Is there maybe a way to find out by opening the case?? "

i don't think so as the serial number is between the lugs...and inside on the movement will just have (rather should have, assuming it hasn't been frankened by parts from a cal 11/12 from another brand??) a bridge stamped "heuer, cal12" and on another bridge you'll see "seventeen, 17 jewels, unadjusted, swiss" that's about it.

i should add, i'm not 100% sure that tag heuer can't track back serial numbers from vintage pieces done under heuer before the buyout, but i'm pretty sure i heard/read that before in more than one place from what i consider credible sources...maybe best to checkback and see what one of the resident "experts" has to say.

"Thanks Frank"

j.h.