IMHO you answered your own question.
It is common, ie: not enhanced, because it is succeptable to all the antibiotics that were tested against it.
There are thousands, not hundreds of strains on file, therefore it takes time to analyze and identify the strain.
We don't know if it's common, because the strain hasn't been identified. At least one researcher thinks it may never be identified.
Maybe the Fort Detrick guys are using "common" and "naturally occurring" interchangeably. I don't know, but I wish they'd use more precise terms, and stop treating us like we're proles.