And how many deserve to be?
Most are probably fly-by-night and suspect, selling nothing.
How many claim to be reflected in charts but aren't?
And how many actually pay royalties?
It's an area fraught with potential problems (let alone criminal behaviour).

I heard a few months back that MCPS/PRS had let about 100 JOLs for UK use. There may be a more up-to-date press release.

My understanding is that there are about 16 digital retailers reporting to the OCC. (They are listed on OCC's online site). Though I believe there are more reporting as some sites provide the service for others. (E.g. OD2 link to mycokemusic, tiscali, msn etc.).

Is that enough? I don't know, but I suspect, like high street retailing, it's prohibitively too expensive to collect the sales data from every outlet. The charts are a sampling exercise. So as long as there is a broad range of sites supplying data, then that should provide us with the charts we require.