Doppel Anastigmat Symmar f:6.8

I understand the Schneider-Kreuznach Doppel Anastigmat Symmar f:6.8 is a Dagor copy with 80 degree angle of view. I have three of these:

1) F = 12cm with serial number that dates it to 1937, in a rim-set Compur shutter,
2) F = 24cm with serial number that dates it to 1942, in an Ilex No 4 acme synchro shutter,
3) F = 27cm with serial number that dates it to 1928, in dial-set Compur shutter,

How long was this lens series produced before the introduction of the "modern" Symmar.
I don't see many examples available on Ebay. Are they rare?

The VM says the dagor type Symmar was discontinued in 1954, contradicts itself and says some focal lengths were available into the 1960s, possibly as new old stock. That's the VM.

Rare? I dunno. Certainly less common than the f/5.6 convertible Symmar.

My understanding, based on unfortunately "here say" info, is that they were a slight variation of the Dagor formula. What the term "slight variation" implicates I am totally not sure of. I'd postulate to say that they were of the classic Dagor formula and should perform just as that.