K flight crew visit maybe two, three or more locations each day of their flying duties but that isn't the point, it is where they report for duty that counts and, as I recall, RYR wouldn't appoint them a fixed base, they would 'float' between bases (because RYR were too tight to pay for crew positioning, hotac etc.) and one month may be working from Germany, another month from UK, another month from Italy etc. etc. etc.
When I started I recieved a letter from Brookfield with an assigned base. 95 % of my flying was done out of there. There's little doubt as to where I was based. There used to be a little group of pilots known as 'floaters' which would fit your description better and without an assigned base. That changed a few years ago. Perhaps after pressure from EASA (or their extended arm, the IAA) about the little piece of legislation 'every crew member shall have an assigned base'. Following the change they were rostered as deadheading out of their new assigned base (likely the one closest to where they're living) for flying duties in another base.