Severe disability premium refusal - not a decision so no need to notify?

PIP reinstated on mandatory reconsideration and it was apparent that the client should have had the sdp.

Letter sent to DWP explaining that he met the criteria from x date; please look at an award.  Some time later I phoned the DWP to check progress and was told that the sdp was not payable but as it was just a matter of there being no change in entitlement it was not a decision and no decision would be issued notifying the client. 

(Reconsideration was requested, it was accepted that the claimant met the criteria and the sdp is now being paid).

I have now been told by 3 people including a supervisor that this is policy.  my client is OK but

1. I wonder how many other people have missed out
2. but on the other hand the absence of notification means that the time limit does not start running so challenges will not be late.