The Contax I was released in 1932 and anticipating the release of the camera Zeiss of course already made lenses for it since 1931 - this includes some small one-off batches of the same lenses for Leica - I assume to be able to test/prototype them without having a camera body ready. This is all in their manufacturing books. So the claim that "there was no Contax then" is counter-factual.
Secondly, the Contax I is not the most user friendly camera, for sure. Also certainly not most the reliable. That didn't stop people like Ansel Adams and a couple of others from making use of them, however. Zeiss realized the issues and quickly followed up with the Contax II in 1936, which in a world first combined the range- and viewfinder into a single eye-piece which sped the composing and focusing steps up enormously.
This model, then saw wide-spread adoption among many popular photographers such as Capa, Ansel Adams, O'Keefe, Walker Evans, also the entire curio of Life photographers including Gene Smith (who also shot Leica) etc.
Lastly, image courtesy of RFFs own dexdog, here's a Zeiss original LTM Lens from 1933. The knurling had been criminally filed to make it fit on a M3... Anyway to say that there was no Zeiss glass for Leica or that HCB couldn't have used it just does not represent the facts on the ground.
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