The nice POSTED ON TRAIN postmark is dated 1939, so this can only be SG171/Scott 172a, perf 14 x 13½
The ACSC lists the perf as "13.92 x 13.52 (variable)". You may need to check your perf gauge again, as it can only be this stamp
You have note that most all Scott perforations listing are rounded. For older issues, it is often rounded to the nearest half so not always close.
This stamp should be a Scott number 172 or 172a but the perforations are 14 x 14, not 14 x 15 (172) or 14 x 13 1/2 (172a).
So how would you categorize it?
re: Australian stamp Scott Number?
The nice POSTED ON TRAIN postmark is dated 1939, so this can only be SG171/Scott 172a, perf 14 x 13½
The ACSC lists the perf as "13.92 x 13.52 (variable)". You may need to check your perf gauge again, as it can only be this stamp
re: Australian stamp Scott Number?
You have note that most all Scott perforations listing are rounded. For older issues, it is often rounded to the nearest half so not always close.