No, in case 3 there's a protocol match. In case 4 there isn't. I'm asking why an adapter is supposedly unable to deal with a protocol mismatch. Dealing with mismatch is the whole idea of an "adapter".

If an adapter exists we can categorize it as case 3 for the sake of this discussion. I think you're needlessly hung up on the word protocol when that really doesn't matter.

> I think you're needlessly hung up on the word protocol when that really doesn't matter.

In that case, you've described two situations:

1. Ports are the same.

2. Ports are different.

This doesn't seem like a particularly fruitful analysis.

"could work but won't without an adapter"

The adapter is the downside. And there's no guarantee that the perfectly suitable adapter actually exists.