V'ger KNEW it's full name was Voyager
Harlan Ellison (and some commentators on this board) observed the unlikelihood of a device with the vast capabilities of V’ger being unable to simply wipe away a bit of dirt from its nameplate to know that its name is actually Voyager and not V’ger. The answer to this supposed plot hole is obvious: V’ger simply became the shortened version of Voyager as the centuries passed and it stuck, similar to calling Jonathan "John" and William "Bill." Yes, I realize it’s a machine, but it’s no ordinary machine and it’s seeking personhood and spiritual awareness.