In Part Two, while the player is in a school, a wall of portraits with all the important people in Rapture can be seen with each person's name under their portrait. One of the portraits though is scratched beyond recognition, and only the first letter of their first name is visible: an S. This is likely a potshot towards BioShock 2 whose antagonist, Sofia Lamb, caused some contradictions to the series' previously established continuity.
An unused Splicer model, nicknamed the "Jockey Splicer", was to appear in the second part, but was cut far in the development process. He even had a fully-textured character model.
The Frosty Splicers are re-purposed "Vigor Junkies", a cut enemy-type from the main game.