What does 'many' mean in 'stopping many terrorist plots'?

Yesterday, Andrew Parker, the new head of MI5, spoke out (though not by name) against Edward Snowden and the Guardian.

‘GCHQ intelligence has played a vital role in stopping many of the terrorist plots that MI5 and the police have tackled in the past decade.
‘It causes enormous damage to make public the reach and limits of GCHQ techniques. Such information hands the advantage to the terrorists.
'It is the gift they need to evade us and strike at will. Unfashionable as it might seem, that is why we must keep secrets secret, and why not doing so causes such harm.’

It's interesting to contrast the above with information emerging in the US about the efficacy of the programs whose existence Snowden leaked. Yochai Benkler writes in The Guardian:

In a 2 October hearing of the Senate judiciary committee, Senator Leahy challenged the NSA chief, General Keith Alexander:

Would you agree that the 54 cases that keep getting cited by the administration were not all plots, and that of the 54 only 13 had some nexus to the US? Would you agree with that, yes or no?

Alexander responded:

Yes.

Leahy then demanded that Alexander confirm what his deputy, Christopher Inglis, had said in the prior week's testimony: that there is only one example where collection of bulk data is what stopped a terrorist activity. Alexander responded that Inglis might have said two, not one.
In fact, what Inglis had said the week before was that there was one case "that comes close to a but-for example and that's the case of Basaaly Moalin". So, who is Moalin, on whose fate the NSA places the entire burden of justifying its metadata collection program? Did his capture foil a second 9/11?
A cabby from San Diego, Moalin had immigrated as a teenager from Somalia. In February, he was convicted of providing material assistance to a terrorist organization: he had transferred $8,500 to al-Shabaab in Somalia.