I never recharged the system, never touched the system in all that 15 years and 382K.
All I know is that the system still cools the car in hot/humid temperature (at least, it did last summer) as it did when new.
Obviously, during the winter time, the cooling requirements are not equal to what is seen in Arizona, but the compressor is still engaged a few times during winter.
I still don't know how it will operate this coming summer as the warmest we had so far this season in our neck of the woods is about 70deg
jackD