Can they go more than 6mo without resupply? I am picturing a moon base that is only resupplied every year or so. I seem to recall that Mars only comes around every 18mo? I may be wrong on that. The ISS is not a ground based structure. So lots could be gleaned from having a base where astronauts enter and exit regularly. Also, ISS gets a different amount of sunlight. So I don't think there is a valid comparison.
To be fair, the vacuum on the moon is also not comparable to the windy atmosphere on Mars.
There's nothing especially exceptional about going long terms without resupply. One can easily prepare/cycle food, water, and other necessities for years ahead of time. The reason the ISS is constantly resupplied is twofold. The first is because its orbit needs regularly reboosting to stabilize it, so you'll always have craft going there to do that who also bring supplies.
The second is because the ISS is quite tiny. It has a total compressed volume of ~900m^3 contrasted against the 1000m^3 on Starship. Factor in its design of interconnected pods and the usable volume sharply decreases.