Yes, that would be a '79/'80 production.
"Interestingly, the top vent is A code and the bottom vents have B."
This must have been a "thing" for Weber back at that time. I recently sold an SJ that had the same A-lid with a B-bowl. My guess is that prior to this they weren't paying attention to production numbers of lids vs bowls on the SJs. My assumption is that they realized it was important once they were putting out cookers with more than one date-code like this which then prompted them to tighten up production counts and ensure they matched? (shrug)