Wanna bet Danny Boy ??????????
Many times I have been told in the lounge there are no on-departure upgrades available on my flights, even when the CRS says there are, then I watch staff getting called up at the gate being put on into Business class seats.
Which indicates to me they are blocking J seats for staff at the expense of revenue pax wanting to upgrade.
This has been a particular hobby horse of mine for years, it does happen, I have seen it heaps of times.
Try it yourself, just hang around the gate when staff SBs are called up and watch where they get seated !!!
M-S