The Numbers vary but there are more obvious markers too than the numbers. For instance, I got IMM 1-1 on my last two NEXUS kiosk receipts entering Canada by Air above the V-#-#-# line. I've heard (via other threads here) that you can get V-IR or V-RR instead of the numbers for secondary. I've never received a comment or additional screening based off of the numbers and have no idea what they actually convey. I do check them and don't recall any particular number that's common given my travel patterns and number of checked bags being consistent.

V = Visitor to Canada, R = Resident is my understanding as well.