It's only offered in the early fall because that is their slowest time and also hurricane season. They are trying to drum up business since most people don't want to take their kids out of school in the first month. Spring is one of their busiest times, other than holidays and summer, so they would have no need to offer free dining.
Yes, I would doubt that they would extend it to other times of the year, especially given that this year they seem to have presented it in a more limited way than last year.
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