I believe I have forgotten to address this. Can you please explain how you are getting this?

AFAIK the txids aren't in any structure used by Bitcoin except in the inventories. Those might be stored, depends on the implementation. However, when it comes to the wtxids, there is absolutely no reason to store them. Their sole purpose is to simply have a hash of all of the data in a segwit transaction and have that be applied to the witness root hash in the coinbase transaction. There is no need to store the wtxids since nothing ever references them.

Where are you getting numvins from?

Anyways, your formula is wrong if you assume that the regular txid is currently being stored. Rather it should be

N + wtxid + numvins > N

and that is only if you are going to store wtxids which are not necessary to store anyways.