I think he hits it every year. There was an episode where he talked about how once he hits the cap, he basically stops trying and coasts for the rest of the year.
And of course Dwight was doing well enough with the commissions that he was able to afford to buy the building. (I’m not in sales, but I think that if two salesmen in Pennsylvania can do that well selling a low-margin item like copier paper, there’s something wrong with the commission structure. Perhaps they should switch to a more lucrative product, like pharmaceutical sales or some such thing.)
It’s not brought up very often, but Dunder-Mifflin also does custom letterhead too. I don’t know for sure, but I bet selling a company on a custom design and high quality paper stock probably brings in a ton of money.