Many weights (and some bottles) from the early Vasart years end up with fractures. I have an example with a crack through the full centre and I am expecting it to fall into two parts one day! I also have some Paul Ysart weights that have fractures.
I don't think it means a particular problem with the annealing but any stresses that did remain could easily have been stable for many years until, for whatever reason (perhaps temperature or collision) they result in a fracture.