i'm somewhat of a radiation expert, and have always wanted to own a 6542 for my personal testing. Technically, if we knew in general what the activity of the original paint was, i could measure the current activity quite simply and date the watch! it would certainly clear up in my mind any questions of authenticity
radium emits mostly alpha particles and b/c in general alpha particles are "fat" and "slow" something as thin as a piece of paper and certainly the plexi on watches would prevent harmful exposure. however, ingestion or inhalation would be very harmful and could cause major dna damage via ionizing radiation. strontium likewise has been shown to cause leukemias.