Don't have any one source, however it's generally accepted that the Hoffritz brand was produced for them by Merkur & just branded with their name. Hoffritz were taken over by, I believe International Cutlery. The 1950s Merkur slant I have is virtually identical to the 50s "slim handled" Hoffritzs. I've noticed that some of the Hoffritz razors, both closed comb & slant on Ebay recently are almost identical to current Merkur design, which probably places them into 60s or possibly later manufacture. With all the 50s manufactured Hoffritz I've seen the rotating locking device at the base of the handle removes entirely, rather than being held captive as it is in the later models.
JohnnyO. \:icon_razz: