I believe Rolex used a number of differen types of radium compositions when they made these pre-tritium dials. I think not only did they use different radium compounds (which is documented) but also they varied teh amount of radium applied to each dial (also documented).
What i find interesting is when certain vintage Rolex dealers try to make claims about authenticity based on just a Geiger reading.
Only two types of people would do that. An idiot or someone with an agenda.
My point is, I have seen quite a few 6542s in totally original state that have varied radiation readings. To my mind...anything between 0 and 400 microsiuverts is totally possible. Though to be fair, i would only wear one with your level or lower!
.....there is plenty of Rolex documentation showing not only different compounds but also that they applied these compunds in different amounts. Just these two facts alone make it scientifically impossible to validate authenticity by using just a geiger.
When was the last time you had it serviced at Rolex?