I just saw the movie. It seems odd to me that, fluff-wise, they had a 2nd Company captain other than Sicarius. Sicarius had to be Captain for several reasons:
- This film is set after the first Tyrannic War (ended 745.M41)
- It is still the 41st Millenium (as stated by Severus during the monologue over the title sequence)
- Sicarius is still Captain at the end of the 41st Millenium
They could have had Severus as some guy sent in the Captain's stead, rather than Captain himself. If that was the case, they could have mentioned that. Then again, this is the least of the oversights in the film.