Next cruise is wrong, simple as that and it does not surprise me. The letter that came out was very clear that as long as the PPG are added to the booking prior to sail date the lower rate will apply.
Here it is direct from the letter.
"If youβd like to pre-pray your gratuities at the current rate before your sailing, weβre happy to extend this opportunity to you. If youβd prefer to pay onboard, your gratuity charge will be applied to your onboard account at the new rate."
Next cruise has always been employees. I know the shops are contract. Not sure about casino and photos and look at it as something that has no impact on me