Interesting discovery: as they produce regular-series plates in advance (and not when someone request one), now that they have several plate formats they had to find a solution. It seems that the "square" plate was produced for the 1-AY*-*** series. See this Skyline:

Normally they only reached the 1-AH*-*** series now.
My father also saw a van with a AY* plate (but only the front, we suppose that a the rear it has a square plate then).
And about the VW shown above, in addition of the long plate he could also ask for the small plate, which should fit in any US-plate size like old Belgian plates; see page 5 of this document: http://www.mobilit.fgov.be/data/div/ekpiepresf.pdf