I don't even know if the Sheraton still has that sunken Four Points bar downstairs. It used to have a glass floor in the lobby that looked down into the bar. For an airport hotel bar, it was a load of fun, and I once had Visa cancel my card there because of "excessive unusual activity".
At some point in the SLC lifecycle, somebody decided they couldn't bear to simply increase the SLC-5/05's Operating System number to 503 or 504, because those were already names of controllers (and so were 501 and 502, but they disregarded those). And certainly they couldn't just keep incrementing the Firmware Revision Numbers.
So they added Series letters to the operating system, and everything came unglued because generations of A-B users were accustomed to Series letters being for hardware only.
It sounded like a good idea, at the Sheraton downstairs bar.