Rondo seems to be away from his computer, so I'm going to have to take full author-i-tie on this one:
FASCIST COMMISSIONER RULING
You can select a seasonal beer to serve year long - but you're taking the whole line of beers.
For example, if I wanted to serve Sam Summer all season, I'm taking all of Sam Adam's seasonals and just opting not to sell the others.
You can't take a seasonal beer that's already been selected.
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Clear?