Just to note that BE have never operated a Dundee-London PSO and the Dundee-London and Dundee-Amsterdam services were never operated by the same aircraft:
The London PSO has always (during its life span as a PSO funded route) been operated by Loganair, usually using 30-odd seat Dornier 328 or Saab aircraft. For a period the route was, of course, operated under the flybe franchise, but it was always Loganair underneath.
The Dundee-Amsterdam service was a totally separate thing, operated by flybe themselves with a Dash-8 (I believe on a W-pattern using a BHX-based aircraft?).
As such, during the life of the Dundee-London PSO operation, the Loganair aircraft allocated to this has never been used for any regular additional scheduled flying in between the London runs.