Not that I have ever heard of. I think you may have one with an unoriginal neck. With that said...if it IS a bonafide Zeph Alto neck....and they were quite a signature design, particularly the key....then you are cool.
I have even used VT-II necks on Zeph bodies and they worked fine since the necks are the same bore and taper. But better to have an actual Zeph neck on a Zeph...even if it may not be the factory one.
Odd situation...that almost never happens...but give kudos to someone, somewhere, sometime... who managed to find another Zeph neck for the horn in question......
How off/close are the serial #'s ????