No need to check the 19V, I was trying to see why you had low V+ and V-rails, but it was the DBT.
The offset is handled by the differential pair, correcting it on the fly until stabilize, as a "servo" circuit: if DC goes up, one transistor starts to conducts more and DC goes down. If it's negative, the other transistor starts to conduct more and raises the voltage. In theory a perfect match in hFE should have better performance. But sometimes swapping transistors can correct the offset (perhaps one transistor conducting a bit more has a beneficial effect). I had good experiences sometimes just swapping the pair, reversing the position. Sometimes the offset increases, sometimes it goes lower.
In some amplifiers, the offset was part of a poor design , and I had to modify one resistor to make it work better, that's why I tell you to leave it alone if it doesn't get better swapping a couple of transistors. 50mV is fine (I've seen service manuals asking for "100mV or less")
I think you got it fixed, so don't worry too much about the offset, I wouldn't be too curious, you can break a working amplifier in a wrong movement.