And it is a reasonable question to ask for the sake of those who have to depend upon it for their and their pax safety, when did the Mk II become airworthy - or not?
Not only a reasonable question C240 but one which in any sane world should never have to be asked. The whole point about the UK Military Airworthiness Regulations is that they be adhered to totally by competent and honourable people. Here it seems neither requirement applied and consequently in order to cover up the initial gross unairworthiness of the aircraft it was felt necessary to cover up the measures taken to then make it functionally safe. Note that I do not say "make it airworthy" as that is a different matter. as airworthiness requires an audit chain from beginning to end, and once that chain is broken no aircraft could be deemed to be airworthy. Hence the dilemma of the MRA4 (still awaiting RTS) and any other type derived from such a broken "Build Standard". I suspect therefore that the answer is "no, it's not airworthy but it's now functionally safe", which with any luck applies to the other military airfleets. Luck is of course no way to run a whelk stall let alone military aviation and that is the job of the hapless MAA to resolve. It will be of great interest to see exactly how they mean to resolve that conundrum.