Sounds to me RT that you are just attempting to grind an 'headless axe' I'm afraid.

As others have said it's clear such boasts by this site are just advertising, if you can do free searches and presumably contact them & ask before payment then you are gambling you'll find something surely?

Take a look at the TV adverts next time you're bored and you'll see almost any advertisement can be seen as misleading if you choose to take everything they say as 'factual' rather than merely opinion:
biggest -biggest in what context, in what theatre?
best - how can you substantiate that?
etc.

I've used this site along with others mentioned here and there's nothing which makes me think they are part of any other organisation, equally a site that offers free registration is pretty obviously going to have 90%+ free members hence your math does not add up.
£22m? no chance.

I'd judge the site against it's peers, and look at their sources to see if they were likely to have something the others didn't.

If other (larger) sites don't have the records you are after it's likely they don't exist in the public/commercial domain, if the other sites offer a full refund and apology if your gamble doesn't bear fruit then I'd agree with you, however I've just checked and they most certainly do not, so what's the beef, really?