The photo is the original 1970 advertisement / article for Beta21 in the horological reference-magazine Europa Star (no. 117, 1970) and it might not be very interesting on first sight, but on second for sure: Bulova and Doxa both were made in 18K solid gold and they were heavy, yes -- the Bulova Drivers-Watch is probably the heaviest Drivers-Watch ever made and for sure the heaviest Beta21. The Rado was made in Steel, only. With a interesting stone-dial and a beauty as well, for sure.
The point here: Neither me nor colleagues, all deep in the Beta21-topic have ever seen a Doxa-Beta21. Of the Bulova I know of just two examples and only one with the original bracelet, done by JPEcoffey.
But the Rado-Beta21 I have seen in at least 10 examples. Of course, it is made of steel and thus was never smelted. Given all three were done in approx similar quantities and the observation is correct, then in a simple derive it comes out that 80% (Bulova) or even more of the heavy gold-watches of 2nd tier brands (ie. Non-Patek & -Rolex) were smelted in the last six decades.
Sure, just a rough estimate but this might give a understanding of how endangered these heavy gold-watches are.
Interesting to note: This research / understanding is so far a complete greenfield in horology, imo. It is obvious a lot of important watches were smelted in the last decades, but so far I cannot see a reliable estimate based on research. And it might be interesting to put some light with serious research on this, to better understand a) the damage done and b) have an idea about the number of left examples.