A check reveals lots marked as Cancelled on RTT now - so either the messages were sent late by GTR or there was a delay in RTT processing them...
The TOC doesn't send messages to RTT.. RTT doesn't have a feed from Darwin/ Tyrell which means that trains won't be shown as cancelled until the Network Rail controller cancels them off in TRUST. This isn't always seen as a priority activity and thus can sometimes happen sometime after the decision to cancel has been made.