I thought you had said above that Lukas fixed it / it was fixed in a patch. Is that still correct, but you had already moved on to starting fresh for 1974? Just curious. At any rate...
First off, my guess is that your affiliated teams don't have enough players because you're not in the regular season yet. IOW, those players are still on expanded rosters elsewhere in those (LA, SD, Oak, Cinc) organizations, and if you were to advance the game to MLB opening day, your NWL rosters should be full.
That said, you are most-likely wanting
accurate 1974 NWL rosters, which is why you need to unaffiliate those 4 NWL teams (Bellingham, Walla Walla, Lewiston, Seattle) from their MLB parent teams. You should be good to do that right now (so no, it's not too late to do that, from what I can as to where you are in the league) by going to OOTP Menu | Game Setup | League Setup tab | Names & Affiliations tab, and then selecting the NWL. From there, you'll see where half the teams have an MLB affiliate and the other half have "none." Change the four affiliated teams to None.
Then just follow the other steps from earlier in this post:
2) Create a separate manager for each team (all 8 teams in the league) and have that GM/manager control lineups, promotions/demotions (from the reserve roster).
3) Go thru each team's roster, comparing baseball-reference.com to OOTP, and move players as needed so your rosters are historically accurate. For the teams that were already independent/unaffiliated, you'll find that their rosters are already pretty accurate. For the other four teams that were affiliated (and you just unaffiliated them), those players may be scattered about the organizations of their initial affiliation.
4) You may or may not need to lock players to rosters in order to keep AI managers from releasing some of them.
That should do it. I highly recommend saving a backup before you make these changes
