I think the 6 and 7( 14 and 15) they don`t call them reserves in Poland can have up to 6 or 7 rides- depending on if RR is being used and if they are 6 down.
the 6 and 7 have there rides protected and the only way they can be replaced is that the team is 6 down and the other one can take his place- If the no 8 is Polish U21 he can also replace a 6 or 7 at any time.