Edit capture time fails after second set

"after that it only changes the first image's capture time."

Make sure you are in Grid view (many thumbnails showing) rather than Loupe view (just one photo showing in the main panel) when you invoke Edit Capture Time.  In Loupe view, the command will only work on the current photo.

"changing the year to 19xx year frequently refuses the input, when after the 2. digit it clears the year field and has only 2 digits left."

You'll have to type the four digits more quickly. It's a longstanding problem with the underlying Mac library for entering dates that Adobe never worked around.