Great write-up! Looks completely correct. Code is here and I also have the same interpretation as you. Basically upgrade mode is a lottery system for early adopters -- everyone who had a node was eligible, and nodes can get more than one payout during that period.

That period is now over so it's in queue mode now.

https://github.com/SmartCash/smartcash/blob/1.1/src/smartnode/smartnodeman.cpp