I agree, WhatPub is an excellent resource. However, do treat it with caution occasionally. I've used it to help plan a few events, such as our annual Easter Pub Crawl, and discovered that, of the two pubs in Normanton which it listed as doing real ale, one had had the hand pump removed, and the other clearly didn't often sell any. The moral of the story - don't bother going to Normanton if you want decent beer!
As with any other resource, WhatPub is as accurate as those responsible for its upkeep can make it - but in this case, such persons are usually CaMRA branch members, who do not always have as much "spare" time as they would like in order to maintain a totally accurate picture. Things do change - beer range, opening hours, a new licensee, or example - and there is not always a CaMRA member "in the know" to update WhatPub immediately.
On the entry for each pub, there is a paragraph which reads:
'Seen some incorrect or missing details? Fill in the feedback form to submit your updates.'
The words 'Fill in the feedback form' are a hyperlink, clicking which will generate a pro-forma for the user to complete, in order to detail the error/omission. Clicking 'Send to CaMRA', at the bottom of this pro-forma generates an email to the nominated contact(s) for the branch in whose area the pub is located. They will (or at least should!) check out the information, and update / correct / create an entry where appropriate.
(and please let's not get into the semantics of how you can "see" "missing details" - that topic has been done to death at several CaMRA branch meetings!)