Depends if it says anterior-most leg, or anterior legs (plural). If it says anterior leg (singular), then that is unclear. Generally though, anterior would likely mean the first two pairs, ie leg I and II.
I looked at the original description of both L.nigerrimum and L.violaceopes, and neither paper obviously mentions a retrolateral brush. So, i cant say about that characteristic, but you are to be looking at the outside (retrolateral) of the anterior legs for that..