Hi, I'm new here and I do hope someone can advise me please?

I've had 2 melanomas in the past, one of them pink, so when I presented with a pink stripe under my great toe nail, I'm glad to say the GP took it seriously, at least to rule out subungual melanoma, although he thinks it's not. I've seen the dermatologist, and today the plastic surgeon who will biopsy me, but now I'm confused, and worried.

He proposes to do a punch biopsy through the nail plate into the stripe. I expected instead that he'd go to the base of the stripe an try to sample the source, which is deep under the cuticle. I queried this and got nowhere. 
What I've read seems to suggest I'm right, that the matrix is the place to look, and I could get inconclusive results from the nail itself.

I could be wrong though if the nail bed also grows out from the matrix, accompanying the nail to the tip of the digit as it grows, in which case, if there is melanoma, it may also be present in the nail bed under the stripe?

Can anyone who's had this done to rule out melanoma please tell me where on the nail structure they were biopsied?

thanks very much

B