This, just mark the new draftees with a tag on the TL search page as well as their players' page or change the colors of their name, would probably the easiest way to deal with problems like this moving forward.
Another idea to implement would be something similar to what happens when you fire a player, you get a warning pop-up window, this can be done similarly to the 18, soon-to-be 19 years old as a warning when the off-season processing is happening.