Paul,
Plane plotter needs a box to feed it, without the aircraft being captured by a box, Planeplotter doesnt know it is there either.
I have also just noted UPS56 en-route KLX-PHNL showing on RB24 as N583UP wihile Planefinder gives it as NO-REG. Just behind it is UPS32 and neither give the registration and both flights are ASDI.
Closer to home for you I just watched the JBU635 flying over North Bay with registration showing as N779JB while Planefinder has NO-REG, both ASDI. RB network down at the time. Also Planefinder showing JBU415 getting a box feedm registration N768JB but RB ASDI didnt have any registration details.
I have however put the question to 3D Dev and await his reply as I am interested in this as well.
Alan