After doing some digging, and finding the public PKP document again (thanks to an unnamed someone, you know who you are!) here are the results:
KM1 - Is actually, probably, might be a ROJ -- a wild guess would be that these...
S1, S41, REG - …are just simply regional stopping passenger trains, that have their line number added as well (like in Hungary: S60, Z70 etc., Deutschland™: RE 1, RB 7 etc.) -- please note: S1s and S41s are actually classified as ROJs in the timetable that you access from the dispatcher posts (sometimes RPJs, see footnote)**
TLK - Twoje Linie Kolejowe (quick google search did the thing) is basically, again, what I'm guessing is what the passenger would actually see, but as per timetable they are classified as MPEs or "Inter-regional limited-stop passenger trains" … or as we'd call them: Inter Regios.
EIP - Y e s . -- Well, actually, they are EIJs or National express trains
you get the idea
If you're really curious, just look at the 10th page onwards in this .pdf that I hopefully attached to this reply. I believe that the timetable will always reflect the proper type as per PKP classifications, since... well... it's a simulator with that kind of attention to detail
** if you've driven the S1 and S41s enough, you might've noticed, that the S1s don't stop at every station towards Myszków, only the S41s do that, and on the other way, the S41s don't stop everywhere, but the S1s do towards Katowice, which is why they're classified differently in the dispatchers' timetables - then again, the timetables will be changed after some time
zal_6.3_Reg22_23_v8_EN.pdf