I thought you were onto something with number 1 under Sherbrooke indicating this was Sherbrooke, Que I (RF 1), so I had a look at my squared circle strikes. Sadly I think I have found more questions than answers.
I found 3 different strikes with a similar numeral directly under the city name. Here are my stamps/strikes;
#36 2-cent SQ has a Winnipeg Type II with a numeral 2 below the city name. This example fallows your inference and seems to be the Winnipeg, Man II (RF 1) strike listed in Unitrade.

But...
#53 3-cent Jubilee has a Kingston Type II with the numeral 4. The catalgoe only lists Kingston, Ont I, II and III.

#51 1-cent Jubilee has an Ottawa Type I with the numeral 2. Again, the catalogue only has one Type I listing for Ottawa.

So the numerals below the city may not coincide with the roman numerals listed in the catalogue. Now I am wondering what they are for. And I apologize that I have done nothing to answer your question about the Sherbrooke strike!
EDIT: But wait... the York Street Type II I posted in another thread bears the number(s) '6
·30' which I assumed was the time. Now I don't know what to make of it! The single digits in the other examples
could indicate the time of the strike, but I think they would use a consistent format and include an AM/PM or use 24-hour formatting.

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~therealwesty