Don't put to much on this AD, as this has been known about for over two years or more.
You will find that this task has been in operation for a few years and BA may have been doing it on its B777 fleet.
I was at a Boeing engineering committee a few years back on the B757 series and we were told that a new task was being introduced to carry out a fuel suction test, which we voted to accept.
I remember way back this being done on the old B737-200s and we were told at our meeting it had come about from findings on the B777 fleet. Due to the fuel system on the B757 being similar to that of the B777, it needed to be brought in. We discussed the interval that was proposed and made amendments to the interval and was as l said accepted.
We were told if we accepted the task, it would mean that it should not have to be made an AD. This task was introduced into our "C" checks two winters back.
So if the same thing has happened to the B777, l would guess it has been carried out for a couple of years.
The main reason for the task, is when you get low fuel quantity you may suck air in, if the fuel pipe seals are leaking. You need a very low fuel figure in each tank to carry out the check using engine runs or you have go into the tanks and use test equipment instead to check the piping.