Yeah and that's why I thought I was golden unlocking everything. Even though I'm pretty full of good maps just under the highest tier I've done I'm still nervous from 2013 where you could be running high-tier maps and just get a string of bad luck and be stuck at pleb-level. The % bonus is a really good feature to help keep the tough content rolling.I only run shaped strand and shore and my bonus is at 91%. I completed every T1-T10, skipped all but one T11, skipped all T12, skipped all T13 except 1, skipped all T14, did all of the T15's, Guardians, and Shaper.
Tuco the more maps you complete the "bonus objective" on it raises the % counter in the center of your atlas. Then when maps drop for you that % bonus makes it so that the map that just dropped has that % chance to drop 1 tier higher than it would have.
Fuck it I don't care I'll unlock everything I can and seal shit-tier maps:
Apprentice Cartographer's Seal
3 sextants and an orb of scouring.