In case we can research it was done because it was demanded by the authorities of the marine, or just the way their watchmakers handled the watches, than it is authentic for me. We are talking here about a issued watch, so, for me, everything that was done to this watch within the time it was used in military, is authentic, especially when it was done because it had a reason why it was done, as it was done.
Sure, a watch in the condition it was issued will be more collectible, no doubt. I think, because this thread was opened for research, we should try to evaluate why there are MN watches with this dial.
It would be interesting how long they were used, how the watchmakers repaired/restored the watches and probably if there were some restrictions on radium at a later point.