Refrigeration engineer. 20years in the trade.
Specializing in commercial, industrial , transport and defence aviation flight A/C systems.
If your "topping up gas" you are sloppy.
No system these days should ever be "topped up" with refrigerant.
And compressors "run dry" when enough refrigerant has leaked out of the system and the compressor pumps oil out into the system to try and balance out the lack of refrigerant in the system.
This does not happen on modern car ac systems as the system has a low pressure switch on the "low" side of the system to protect the system.
If a system is gas tight it should never need to be serviced. EVER.
The reason you need to run the ac monthly is to lubricate the carbon/ceramic seal in the fromt of the compressor.