Thanks AT,
Many years ago I heard a virtually identical story about brand new Halibags begin test-flown for the first time immediately before scrapping, though I cannot remember where that was supposed to have taken place. The explanation I was told was that the contract to build them (not surprisingly) required them to be delivered in airworthy condition and, upon delivery, if any were found to be unfit to fly, the Air Ministry was able to avoid paying for the airframe and could simply reject it. If the aircraft was deemed airworthy right away, it was considered 'paid for' and then (sadly) sent for scrap. Don't know for sure if that is true, but that is what I was told and it would seem to fit in with what you remember. As you say though, it doesn't explain why old ones were kept and new ones destroyed. Could it have been something to do with whatever mod state was required by the airline? Just a guess...
Ed
WHBM,
Excellent, thanks again!