Langford V Rowling? No contest
Langford (nice bloke, deaf as a post) has been in the business far longer than JK and knows a lot more about the field than she does. If anyone can reliably pick out the many sources that have "inspired" the background and plot of the Harry Potter books, it's him. Rowling is a literary lightweight despite her success and Langford has probably forgotten more about fantasy writing that she'll ever know (or admit to knowing for that matter).