Re the getting rid of 4, 7 etc, do you think it could have anything to do with getting rid of single digit route numbers which may have caused problems with early computerisation of head office work like Table or Timetable prep?
That does not fit with the retention of roue numbers 1, 3, 5, 6, 8 etc.
PT authorities know that changes in route numbers upset passengers (aka customers) so they don't change them without much bthought.
Mal Rowe - surprised to have found that route 59 was originally allocated to Somerville Rd to Footscray!