Given the number of scripts actually available in their library, it is obvious that their claim to being "the worlds largest script library" is wholly false - BL offer access to a larger number of scripts.
I see no such claim: their claim is:
We also have the most comprehensive on-line dancescript library in the world!
I don't know of a larger one - certainly Brockbank Lane have exactly NOTHING online, and they will only supply older scripts, by post, to subscribers to their current script service (£39pa + the cost of any older scripts, as ordered). You can't order and pay online, either, because they do not accept any form of online payment, which a particular nuisance if you are a non-UK customer.
As far as I know, B-L doesn't even have a website. Seemingly, the proprietor is retiring, and the business is for sale. Their marketing methods certainly need a rethink, if the business is to have a future in new hands.