If you want a Sago with a clean trunk, take the puppies off the minute you see them. The only reason to leave them is if you want a multi-trunked tree or you want to propagate them. Removing the larger ones will leave scars until the trunk heals. You can usually take them off by twisting them or cut the stem between the pup and mother trunk.
Pups grow but, you can limit the numbers by keeping the trunk dry.