Ah, I should have been a bit clearer.
I totally understand what tolerances are and I'm fine with the measurements being off when they are still in the tolerance.
OTOH, it feels much better to actually know
why the measurements are off. I always want to understand everything. I'm not asking for advice, just information.
As far as I understand the circuit, there's only a low pass filter between the rectifier and the heater, so the voltages should be approximately the same, except that they are filtered on one side and unfiltered on the other.
So (assuming I didn't screw up the measurements) my only explanation would be that my meter isn't very reliable if the voltage is not filtered. Which would again imply that I have to take all DC-measurements of my meter that are not known to be constant voltage with a grain of salt.
But I also understand that this isn't support for your products anymore, so don't feel obliged to answer.