Hi TCF,
I agree with you. If the cabin altitude (say 3,000) is still above the destination altitude (say sea level), then with a very rapid aircraft descent rate down to sea level, we may overtake the cabin altitude.
When the diff pressure is zero - the inward relief valve will open and the aircraft and cabin will have the same descent rate.
Maybe that's what tg743 was alluding to. By increasing the cabin ROD down to sea level at a comfortable rate (700 ft per min say) then they avoid overtaking the cabin altitude on the descent.
Sorry BOAC, but have TCF and I missed something again?