I think all the guys except Richie have had some sort of hair extensions done.

Take a look at Helter Skelter/Something for the pain form the 1995 VMA: Tico has a bald spot. Gone now. How about the OWN single cover, those are definitely hair plugs in the front for Tico.
Pop in the Crush tour dvd: clear bald spot for David. Gone now.
Jon had a BIG bald spot in 1996, four years later it was gone.

It's just impossible for receding hair to grow back like that (as a balding man myself, I wish it was). Tico should always wear the buzzcut like he did during the end of the Lost Highway tour, makes him look much younger than the forced plugs/slicked back hair he usually sports.