It would be a safe bet to assume that no vintage watch is water resistant.
There are exceptions, and usually these are dive watches that feature screw down crowns. For any water rated watch to retain its original rating, it must be serviced every 1-2 years and have all the gaskets replaced.
This is the official line direct from Breitlng. In addition, hot water will void any warranty and rating, partly due to the fact that rubber shrinks in heat. The watch may exhibit water resistance for longer periods of time, and they often do, but in order to be warranted for water resistance it must be serviced frequently.
Vintage watches were rarely, if ever 'water-proof', and in fact the term is no longer used. Water incursion is usually through the stem on these non-screw crown watches, but failure of the crystal, or crystal gasket (if there is one) is also a possibility, as is the failure of the case back gasket.
I always tell my customers to assume their vintage watch it is not water resistant. Old watches will also 'respirate'. Wearing your watch warms it right up and it will expel a minute amount of air, and if you take it off, it cools. When it does, it starts to suck ambient air into itself. This is a microscopic amount, but if that air is steamy from a hot shower running, the watch pulls that right into itself. So if you take off your watch to have a shower, placing it on the bathroom counter, it may well respirate some of that moisture. I see this a lot.
In addition, a watch will always have air inside it, and whatever the amount of moisture the air carried at the time the case was closed is now trapped inside the watch. If the watch gets cooled suddenly, like in a cold rain or being dropped in snow, it may condense water on the inside of the crystal. This is also what it may do if it has leaked, but it is best to get it checked out.
For vintage watches, it is best to keep them away from water, and cover your wrist if you are caught in the rain.
The vintage watches we see here are often not even dustproof, so extra care is needed when wearing these.
As for this fascinating watch, the fact that there are two of them in Dennison cases suggests that it may have been a normal occurence. I suspect this is due to the fact that it is a non- North American watch, and this may indeed turn out to be a UK thing on its own.