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They really look like 60's posters. I just included the 50's because some of the posters are actually from the late 50's. In fact, the left one you linked advertises an event happening on "dienstag, 5. mai 1959". The right one seems to be from 1959 too but I'm not sure.

The colour palette for me has a bit of a dated feel, although I assume these are scans of the originals and would probably look right at home if freshly printed.

I think it's the writing too. All-lowercase writing was more common in the 60s and the font[1] is not that common today.

[1] https://www.myfonts.com/fonts/castletype/standard/medium/ according to Whatthefont

It reminds me of Broadway Boogie Woogie which is from the 40s…