Another worthwhile distinction between the two competitions to bear in mind.
In both, U21 players don't count towards the 25 man squad. In the PL an u21 player is simply a player who is U21 in the relevant season. In the CL, an U21 player has to have been with the club at least two years, to count as U21/ B-list.
So the likes of Reis and Echeverri are fine in the PL, but in the CL take up a NHG squad space.
But this is nothing new, we had that with Zinchenko, Jesus, Balotelli, etc. None were left out of the CL squad, we just went with fewer players in the NHG category to include them.
Most often when we had 5 or more HG players, we then had 16 or less NHG players. So eventhough we were under the 17 limit, we were at limit overall. If that makes sense.
One thing is certain, as long as the club have neen in the CL, our squads have always been built to meet that criteria. Don't see that changing this year, myself.