I think I understand a little better now. The chance to pick perks you get pre-Mosaic qualifying kicks in after every 10 tiles (I think these perks can be superseded by subsequent picks - you pick one at 10 tiles that goes away if you pick a different one at 20 tiles).

Once you reach Mosaic, you get one perk you pick that lasts through your Mosaic tenure. If you reach a higher Mosaic level, then you get another perk you pick that lasts through that Mosaic tenure. But consumable picks -- 20 tiles -- are just used/applied. You don't get additional perks you pick at the 60/70/80/90 tile tiers.