I just unpacked my PRR Centipede; its been away for about 18 months after the move. As I was putting it on the shelf I noticed that both units were numbered 5823. I didn't remember that they were like that. I looked up the description on the MTH website; but didn't find any info. Wikipedia had a description and roster of all the units. The first PRR set was 5823A1,2.
I think that the follow text explains why they would be numbered that way. The reference to a single carbody and steel half-frames seems to denote a single unit.
"The carbody rode on two massive articulated cast steel half-frames cast by General Steel Castings, linked at the middle with a hinged joint."
It appears that PRR eventually renumbered the units in sequence.