Pretty much thats the official story the restart the numering but honestly, those times are a grey shaded area.
Originally Posted by brucemuir
I happen to have Zeiss-Opton Nr. 26***, non coated, on camera made 1938.
Also, some of the post war Opton have issues with the canadian balsam.
Years ago, I was cleaning a Super Ikonta Opton (Tesar) lens for a friend, one cemented group had a tinny bits of fungus on the side.
Around that post WWII time, Leica had similar issues with, again, canadian balsam, M2, M3 prisms, Summicrons an we can go on up until late 50's.