Not that I know of. Cytowic doesn't cite any authority for number forms having been upgraded to synesthesia. He may have worked that out with Eagleman, and declared it to be so, there being no more recognized authority than him (Cytowic).
Since synesthesia is not considered to be a pathological condition requiring treatment, I suspect there's probably no urgency about consensus on criteria. Also, it's only been seriously researched for a pretty short time so I'd suppose all the researchers want to keep things open ended until more is known.
I don't know if you're familiar with the Diagnostic and Statistical Manual of Mental Disorders. It's the authoritative text used by all psychiatrists for classifying mental illnesses. The thing is, it's in constant flux: important changes in every new edition. If there were ever such a guide created for synesthesia I am sure the same will be true: new research, better logic will keep it constantly changing.
Given the experience of Jim McNamara having been brought to a shrink by his parents to cure his number form, I hope synesthesia gets included in the DSM to alert shrinks it's not a mental illness.