Why does hp e3610a has two pass transistors?

[Farrow]

I'm learning all the ins and outs of a linear power supply. Trying to design my own, reading Hp's old power supply app note (Very helpful). Im trying to replicate the e3610a psu and by looking at the schematic I see they have ditched the mosfet approach and switched to a more conventional darlington setup. but I'm getting confused here, are they using both darlingtons in parallel to distribute the power dissipation or using one as CV and the other one as a CC pass element?

[SeanB]

All 4 are in parallel, in 2 strings of 2 parallel transistors, likely done so they can easily have current limiting for each pair of 2, and 4 overall because it reduces the heat dissipated in any transistor, plus also allows them to offer a lower current units with the same basic circuit board, only changing the transformer and removing one of the pairs. That way the designers only have to match a pair of transistors at a time, and thus makes assembling easier. You can see the entire drive circuit is duplicated from Q2 to get the 2 drive circuits.