Waterproof versus water resistance.
50 meter is as you mentioned not a watch for swimming.
Water resistance is only a guide not an insurance water would be kept out of the case.
100 meter is swim proof and a little depth under water. The shower watch.
This would be lower when a watch was opened at a service center.
I tested two times a 5 AT water resistance watch without a screw in crown in the shower, and the watch was fine after the water test.
I tester ones a 100 meter water resistance watch with a screw in crown in the shower, and here also no problems.
I tester my Seamaster 300 two times in the shower, no problems.
A swimming test i will do when i see a pool.