J.L.
Hi L., I know that's sound strange, but my son is one of those people, so I know it can happened. Tonsils and adenoids can regrow because they are examples of lymphoid tissue. This is the same tissue that forms large lumps in your neck whenever you have a bad sore throat. (Those lumps are lymph nodes.) Lymph nodes can grow and grow and grow ... sometimes to enormous size. Tonsils and adenoids have this same ability; as with lymph nodes, the individual cells that make up a tonsil or an adenoid have an enormous proliferative capacity.
Some body tissues can regenerate (grow back), and some cannot.
If even a small bud of tonsil or adenoid tissue is left behind by the surgeon, the tonsil or adenoid may regrow.
That is how I noticed that something was wrong, when my son start snoring again 1.5 year after surgery. ENT doctor will answer all questions on your first visit. We had to remove his adenoids twice. But it was worth it. He finally got a good night sleep.
Cheers, J.