My fish were in bad shape when I got them. Both tails and fins were in very bad condition. The first day or two after we brought them home pieces were breaking off and lying on the bottom of the bowl. By the end of day 2, there were like little white spikes on the ends of both fins and tails... and now I see that those white spikes were the new tissue... both fish are growing new fin and tails.
Maybe, after the strong ich treatment, your fish is regenerating his tissues? Are you doing anything to the water besides stress coat?