Not to throw a wrench in the gears, but this may be a possibility also...
Sometimes a local will affiliate with a national and the national will allow them to keep their local letters as their national chapter designation. For example, the Sigma Nu chapter at Knox College in Galesburg, IL was founded in 1861 as Delta Theta. They affiliated with Sigma Nu and were chartered 30 years later in 1891. Even though Sigma Nu was in its "Beta series", (after Beta Beta and before Beta Gamma) they allowed the chapter at Knox to keep Delta Theta as its chapter designation. Sigma Nu would not have reached Delta Theta until 1909 at the earliest...
http://www.sigmanu.org/groups/underg...rs/listing.php