Hasn't Cox always inserted the Name Field of their Caller ID within single quotes? For example...and this number is well documented as a nuisance number...from my Cox Call History log: '800 Service' (888) 269-3447. Or is what you're saying is Cox is now using double quotes?
You can't block an invalid number but an invalid can call you: priceless! What do YOU mean by valid...the number contains 10 digits or you looked it up in an assignment database? Probably a dumb question, but is the telephone number in question preceded with the Country Code "1" in your Cox Call History?
I think when Cox identifies a number as invalid, it probably means the number is not an NANP-assignable number. In other words, you can't *60 a fake number. Moreover, if you pound-sign the last call, Cox still identifies it as not NANP-assignable and assumes an out-of-area call within North America.
You're to block the number anyways...so what's its first 6 digits?
I remember...probably last year...the FCC was pressuring providers to create a caller-authentication process to combat robocalls. I think the FCC code named either this push or a specific process as SHAKEN NOT STIRRED...or something thereof. If it is a valid number, perhaps the North American Country Code of "1" marks it authenticated for future calls.
This may be either a recent change or glitch. I'd assume glitch. That's why I hate relying on someone to block my calls.