JohnB - Incidentally, I know your question was directed to GRJ but FWIW I just came across a section in my CAB-1L & BASE-1L Owner's Manual pertaining to Building Trains ("lash-ups") which states the following...
During train configuration, train addresses must be entered as two digits, using a leading zero for train addresses 01-09 (or 01-99 for LEGACY locomotives).
Hope that is of assistance to you.