It's probably an underestimate if you include every possible case. But it's meaningless in itself to simply say that a structure is "vestigial [full stop]". It can only be vestigial with respect to some phylogenetically former state AND with respect to some specific function. Since most structures have multiple functions, a particular structure or organ might well be vestigial with respect to some function(s) and at the same time advanced with respect to others.
Hmmm. Sounds like a rather effecient design. Dare I say INTELLIGENT.