You can only have 1 knot. Unfortunately, Dane doesn't have his multi-knot penis anymore either; it gets removed after Myrellion and is replaced with a horse cock when you find him on Zheng Shi.
It's really disappointing how basically every penis is just a horse cock at this point; most of the cock transformations you can do to NPCs are just turning other types into them. The list of penis types is actually pretty long, but you wouldn't ever know that with how little variance there is in the game (not that there isn't any, but the list of characters with them is short). I was actually pretty excited when I saw the Divrani for the fact the sole fact that they actually have unique cocks, but they don't seem to have any scenes yet (Though if you read the codex entry, you will find out they just have a canine-like penis, the big twisty thing on their crotch and flowers on their nipples being parasites).