If historically unforested land is artificially forested, then that might be worth crediting to humans, but that has never happened on a meaningful scale, and realistically, I don’t know if it could. If deforested land grows back (at whatever rate), then that is just nature cleaning up the mess as it always has, and the amount of carbon dioxide sequestered on that land is always going to be less than what would have been sequestered had humans not slashed and burned the vegetation in the first place. The forest has to recapture the amount of carbon dioxide released by deforestation just to “catch up” before it can continue where it left off, so to speak.