A meets are open for all swimmers to swim.
B meets are for those swimmers that have not bettered the Midlakes B-DQ time for a particular event. (They can swim other events in which they have not better the time.)
Each year Midlakes posts the B-DQ times on the Midlakes website.
This structure carries over to Division & League champs as well.
Any swimmer who has competed in 2 meets may swim at League Champ Prelims, but those swimmers that have better the B-DQ time may not swim at Division Champs.
See link below for BDQ times.
https://www.teamunify.com/reclmslwa/UserFiles/Image/General%20Info/Documents/2015%20BDQ%20Times.pdf