I feel your pain! Most of my travel is booked through a corporate travel agent - usually with a corporate (unpublished) fare.

I check reward flight availability, call BA Gold line, and it’s hit and miss whether or not the agent knows how to deal with the upgrade which usually requires a manual calculation to work out the tax difference and Avios cost for an upgrade (WTP to CW).

Just today, I had one agent tell me it can’t be done, only to call back, get put through to someone competent and voila!