User blog comment:Drache Mace/Who was Yang looking for?/@comment-3257939-20140809211330/@comment-4010415-20140809212803

Monty said he originally made the Red Trailer as something to show to Burnie to get him interested in letting him make RWBY. After Jeff made Red Like Roses, Monty redid and rearranged the Red Trailer to flow with the music better. Back then, he hadn't come up with Ruby's personality yet, and he was more so showing off the basic design he came up with for her and how she wields her scythe.

As for her character design, the only difference between the Red and Yellow trailers is the thing on her belt. It changed from a cross to a rose. Since the Red Trailer was an early concept of Ruby, it makes sense that something about her would be different in a later work. Characters in any series go through multiple stages of design. Hell, Ruby's earliest concept art has a rather different outfit that they seem to have used as inspiration for the one she put on in A Minor Hiccup.