While I know nothing about the B737 Flap Load Relief System it seems strange to me that you would not have know it was activated. Before it was removed on the majority of the L-1011 fleet if the Flap Load Relieving System was activated you would get a light (Flap LRS Limiting) and movement of the Flap Indicator. Which if they were awake should be enough to alert the Pilot (or Co-Pilot) to slow the thing down.
So the question, does the B737 have a Load Relief Light and a Flap Position Indicator? If yes how did you miss them?