I was told at that time the saving grace for the BA crew was that the engines were RR (triple spool) and if they had been US manufacturers then probably not restartable under any circumstances due to pumice damage.
Anyone else heard this?
There are a lot of old wifs tales being told arround ... all of them just speculation.
restarting is mostly a case of setting the right air speed and altitude conditions. Acceling the engine above idle is another thing. There is no such thing as "rugged" when it comes to fine ash sticking to stuff in the hot section.
You're surely not going to hear bragging from the engine manufacturers about running into volcanic ash any more than encountering birds, rain and hail.