It happens A LOT. I just went through updating the database for the rush results spreadsheet and it happens all the time. There are a couple Sigmas at Iowa, as a for instance. But many schools developed Greek systems kind of all at once so especially for the older chapters they will be all pretty close in chapter designation. And true with single letter chapters as well. Cal has a TON of single letter chapters, and if they'd expand they'd have even more since so many sororities had to close chapters there.
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"Traveling - It leaves you speechless, then turns you into a storyteller. ~ Ibn Battuta
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