Tailbound "Classic" is the original demo released in 2019. Originally, the game was going to be a 2D Resident Evil clone that focused mostly on puzzle solving, but I realized that I really didn't like designing the puzzles for the game. The "normal" version of Tailbound uses the source code from my unfinished game, Moontide as a basis for its gameplay.
TB:C has different characters and a different plot, though the main character and overall premise is the same between the two games, hence the different sex scenes included. Plus, the sex scene system was different (albeit, lazier in TB:C) since it was entirely still images and text, while in the final game I went back to Thirstchasm style animations, but kept the idea of having text describe the scene in more detail.
TB:C itself is included in the Deluxe Edition, so you can just play it yourself if you're curious to see what the differences are. I think I included the walkthrough for the game somewhere in Deluxe, but if I didn't then here's a link for it: https://docs.google.com/document/d/1RG8ZWW2Nm8G8wv3Cy5TjD-kw_wL6niLGVF96ypauekM/...