Hi Jack,
This is correct as the first dual plates were brass units as the original brass units were only a one liner and then a serial number was introduced as a separate line, thus the second plate was introduced as an underscore. Now the only confusion that arose was why they did this in ally and not just get the new ally plate made up as a dual information unit from the start. I strongly feel that a lack of communication around the design in the plates was encountered and thus it only changed after stock of both top and underscore plates was exhausted as the company never ever wasted anything.
Cheers,
BB.
