If I am understanding your question correctly, the difference between the two seating stems is their length. Both stems are "VLD" stems with a deeper hole and bevel around the opening appropriate for use with VLD-style bullets that have a very long nose. The length of the stem is about the adjustment range of the seating die micrometer and the desired length of the loaded rounds. I always use the "standard" length stem in my .223 Rem seating dies, but I think you could probably use either one and simply re-adjust the seating die micrometer. The potential issue is that one might exceeed the adjustment range of the seating die micrometer if not using the "correct" stem. In a worst-case scenario, this might necessitate the use of shim(s) under the die if the stem is too long for the chosen bullet/cartridge/die, or render the die difficult to use if the stem is too short. A simplistic way to think about which stem might be relative to bullet length. In a given cartridge, the long stem might be more appropriate for really short bullets, the standard stem more appropriate for longer bullets. Of course, that is an over-simplification as there is more to this than just bullet length, but it's one way to think about the principle involved.
As mentioned, I use the standard VLD stem (#55722) in my Redding Type S seating dies for loading Berger 90 VLDs, Hornady 88 ELDMs, and couple other long/heavy .224" bullets. I've checked the seating die stem hole depth relative to bullet nose length and I may not have to use a VLD stem for these bullets, but I do anyhow. According to Berger's website bullet dimensional measurements, the 90 VLD base-to-ogive dimension is ~.037" longer than the 85.5 Hybrid. Further, my Redding seating die micrometer is set well above "2" when seating 90 VLDs at ~.020" off the lands (COAL ~ 2.6"+), so there should be plenty of adjustment range in the seating die micrometer for the 85.5 (the seating die mic has over 0.2" downward travel left).
Nonetheless, my advice in this situation would be to call Redding and pose the question to one of their technical staff. It has been a long time, but I have spoken in the past to the folks Redding about this exact issue and they were VERY helpful.