Crew Training doesn't have a DP soft-cap.
Yes it does. 15% up to 240 DP of combat ships, then dropping proportionally. Combat ships essentially is everything without the civilian hullmod (and the two phase logistics ships). Although militarized subsystems will make civilian ships count as combat ships for this as well. However, this CR bonus is completely unaffected by the presence or absence of officers. So should be flat across the board.
In a pure vanilla game, CR bonuses can come from:
Crew Training: +15% (up to 240 DP and scaling down, applies to all combat ships)
Support Doctrine: Effect of Combat Endurance on unofficered ships, so +15% to all unofficered ships
Hull Restoration: +5% per s-mod
Combat Endurance: Officer specific, +15%
Max CR Reductions only can come from lack of crew or d-mods.
You can't have 85% max CR on some ships due to crew training and only 74% max CR on another, unless that other ship has d-mods or is not a combat ship. In any case, you can go to your skills screen, hover over Crew training, and it will tell you the current % being applied (along with the DP values). The example screen shot shows a full +15% since I have only 236 DP out of 240 DP combat ships at the moment.
Is this a pure vanilla game, or you running any mods, like Starship Legends? That mod in particular has some traits which are related to CR and can be affected by how many battles a particular officer has been at the helm of a ship, and whether the ship survived or had to be salvaged from those fights.
Edit:
Taxes paid disappear into the ether. It is gamified so that a commerce colony you own doesn't default into the best place to sell stuff.