Before we get too hung up on the 900 hrs thing. On the 4 long haul fleets there are only 82 pilots over 800 hrs in the 11 months to 31st Aug (ie within a fighting chance of hitting 900 before 30th Sept). Some of them probably have leave etc that will keep them well below.
That's out of 2800 odd pilots.
There's only around 300 who'll even be over 750hrs in the same 11 months.
It was much worse a few years ago. 1/3 of the 747 fleet were 'on the list' at one point