allergies are weird things. they can come and go.
Yes, allergic to all shellfish (shrimps, crab, lobsters, clams, etc.) I can eat a few shrimp, or a few pieces of crab/lobster or drink a few Caesars- then I need to stop.
Often, at Chinese dinners, I just eat the crab/lobster sauce on top of white rice. MMMMM. Or the scrapings from the inside of the crab shell.