Sigma Nu had 10 chapters active before it ever had a "beta" chapter. The old chapter nomenclature was Roman Numerals. Trying to adapt itself to be a more "Greek" organization, Sigma Nu adapted the Greek Letter system for chapter name around 1880. Our "Beta" chapter is still active, it was founded in 1871 two years after our founding at the Virginia Military Institute.
If you've ever been to our chapter listings on the Sigma Nu website, that explains why the early chapters aren't in order