Originally Posted by
mikeyfly
It does give extra - but there's no exact science. When selecting if there's additional shown, it'll be dark across the date tab, and a sentence up top to tell you extra availability has been shown.
It's not as clear as I4 = space
if you click the "Find availability with BA on other dates" button on the website, it does correctly show all the dates with the extra availability, assuming your initial search had the voucher enabled