As far as I know, the issue with USRM is not in FDA regulation, but rather in it's guidelines.
Unfortunately, it depends on the FDA's interpretation. Not what the public or medical professionals like myself think.
Here is what the FDA says on guidelines:
Guidances “do not create or confer any rights for or on any person and do not operate to bind FDA or the public. An alternative approach may be used if such approach satisfies the requirements of the applicable statute, regulations, or both.”
In plain english, It doesn't depend on the FDA's interpretation. It depends on the law.
If I remember right the FDA contradicts it's own regulations when prividing guidance on stem cells being a drug.