I believe there are two boards a week at present.
Don't worry about the number of vacancies - you only need one place! TBH, however, I'd be concerned about the fact that you only appear interested in giving it another go because the statistics are in your favour - if you're keen, why haven't you just done all you can to prepare yourself to the best of your ability, and had another go already? Surely it is better to be the best candidate out of a hundred, rather than the best candidate out of twenty? Personally, I'd certainly take more pride in knowing my selection was down to my hard work and innate abilities, rather than a lack of competition ...