I do not have a copy of DBMM Book 4 - but your query was a catalyst for ordering it. I should have my copy on Monday.
I have all the DBM books but none of the DBMM because they were so hard to get. I just realized they are on Amazon. I did not get all the Books, just the one on Book 4 which is my favorite period anyway and where most of my future armies will be built from.
" The rycerz "knights" (alternatively called kopijnicy "lancers") were supported by czeladz "followers", initially armed with crossbow and so called strzelcy "shooters", but by 1400 also with a lance. Czeladz at first drew up in a separate line behind the rycerz, but after 1400 bodies of rycerz and czeladz often alternated in a single line with light cavalry, usually Lithuanians, on its flanks....Czeladz before 1400 and Lithuanian LH can always dismount as Bw (O)."
I've never been so tongue-tied whilst typing in my life!
There is an interesting 6-page article by Matt Haywood in Slingshot 237 about the Polish Army.
The czeladz (post 1450) were indeed a mix of crossbow armed troopers supported by others armed with lance. Firing several rounds of bolts, the lance armed czeladz would charge the disordered enemy; a tactic primarily used against the Teutonic order and the Tartars.