Mark,

It's the only one I've had without a Ref. Number. It is powered by a Valjoux 7730, which leads me to believe it may have been made before 1969. Or maybe it was polished off sometime during its life, the Serial Number is still visible. It's just like the other Tradition 7723 I happen to own, with the exception of the dial, which is a panda.
The caseback is marked Stainless Steel, instead of Stainless Steel Back, as in the 7721 model.

When did Heuer start stamping Ref. Numbers between the lugs?

When I found it, it was missing its crystal, but it was running and keeping good time, with chrono functions working properly.
I had no idea what Stellaris was, but after a bit of research I was able to learn it was just another Sears line of watches.

The dial is a real joy to look at, and I don't usually care for silver dials.
It turned out to be a keeper!

Regards

Darwin