PA-7, PA-7E have two trimpots, one for bias current and another for DC offset.
PA-7_II, PA-7A_II, PA-7E_II has one trimpot for bias current.
But I found a "PA-7E_II 6" pic with two. Maybe post pics of the region with the mystery trimpots. Nakamichi may have rolled back to two adjustments on later board revs. PCB Part No. BA07259A or BA07446A?
Sometimes there are issues with mismatch in the JFET input diff amp. I'm not sure how good the dual 2SK240 was in production, they may have done an update to the PCB and design that is not in the available schematics. Other times I have seen an extra balance trimpot for the JFET front end. That adjustment is not for the faint of heart. A noisy trimpot can cause drama when at the JFET sources.