First cylinder valved in service IS the primary.......lever is pointed to it so porting for GREEN/RED indicator is on primary cylinder
When Primary cylinder goes EMPTY the auto switch over switches over to other cylinder automatically and GREEN/RED indicator turns RED because cylinder and indicator are empty.
Then you swap lever to in service cylinder which ports/resets indicator to full cylinder and it turns GREEN
Indicator was GREEN and stayed GREEN so first cylinder had propane in it.
You did not swap cylinders UNLESS you valved out the first cylinder and then the auto reg. swapped.
Changing lever from one cylinder to other just changes porting on GREEN/RED indicator.
You reset furnace and then it fired off.....on the same partially full cylinder UNLESS that one was valved.