Z class business bookings and concierge service for same-day changes
So I recently learned that concierge service is extended to paid business travel on the same day at the airport. I often fly between LHR and YYZ and have experienced this a few times, where I've shown up very early in the day on a Z or P fare and asked to do a same day change. Generally the check-in agent has directed me to the concierge and this has been no problem at all except on my last trip. I was told the fare rules didn't permit SDC's, but looking back at the other occasions, I don't think the fare rules permitted it either, or there was a $150+ fee, which was waived each time. My employer purchases paid business travel from CWT, and when I requested the CWT rules for my latest trip there's no mention of same day changes.
Have my few trips been an anomaly, or was the one occasion where my request denied the anomaly? What's the norm here? I read in a post on this forum that when dealing with the concierge fare rules tend to go out the window and they have a lot of latitude to do same day changes and waive any fees. Is that really the case?