Thank you GLSNightPilot and Genghis for your comments.
I have done 'calibrating flights' by flying on different headings and noting the differences and making due allowances for any observed wind effect. I am aware that this is rather hit and miss but all my results however constructed seem to point in one direction that PEC is relevant in descent and climb.
Shawn I take your point about the 'snubber' as there is a tendancy for the ASI to 'hold' onto airspeed when quick stops are performed. It is possible to come to the hover with 35-40 KIAS showing and there is a delay of 1-2 seconds before the ASI reads the expected reading accounting for local wind effects etc.
Is PEC given for any type of helicopter when climbing/descending?