From my observations going through the numerous uncirculated $20 Journey Series notes, it seems to me that the Canadian Bank Note and British American Bank Note Printers are printing 10,000 notes (10 bricks) at a time (with same front plate and back plate numbers), instead of the initial 500 notes or 1,000 notes first thought.
The reason for this theory is that I have noticed notes that are 1,000 to a maximum of 10,000 notes apart and they feature back plate numbers and front plate numbers which are identical.
For example, an EYJ note with serial number EYJ6410000 will have front plate #27, back plate number #40. And yet, an EYJ6419999 will have idential front plate and back plate numbers.
Thus, I believe that the printers are now incorporating new printing techniques for printing the notes than we have previously seen .