A lot of it depends on where your house is compared to the path of water. I have been in lots of 40s-50s houses with wet basements. Probably more than 75% of the ones I go in have some moisture. Drainage tile was still kind of new then, and lots of it has failed. It wasn't until you got into the 60s and 70s that homes seem to have gotten a lot dryer in general. The post-war era was really just the beginning of standards in the building industry so there is a lot of variance.