There was other threads on this.
In my experience, and mine only, the validity is the span of time/date before which you must use the credit/minutes, before they vanisb into thin air.
There was talk about the claro phone number/ SIM being desacfivated after a certain lenght of time. I do not believe this to be true.
Why ?
I have the same # since, maybe 6 or 7 years ( yes, yes, I know, not very dominican

). During that time I have being out of the dr for months at a time, once it was 14 months. Back in the dr, topped up phone with credit, and pouuum ! it works.
Disclaimer : i have another claro # that i leave with a sobrina, so i can contact her. She tops it up with 50 pesos once a month. Just to be on safe side. Especially since that # is not in my name. ( to pi$$ off the nosy american big ears

)
Also, last year I visited claro big shop thingy in POP ( which I DO NOT recommend for the faint of heart, or the easily angered ) to get a phone with my point thingys. Well the lady asked us if we wanted to clear some #'s that we had, unused ( apparently u are only allowed a certain number of numbers by name/cedula ). My wife had a # dating back to 9 years ago........