While according to the definition, every inversion of a chord is a voicing and every voicing is an inversion, here on chord-book.com the 2 terms have their strict meaning.
Here are our defintions of each :


Any inversion/voicing of a chord which spans less than an octave (a major seventh or less). That definition still applies even if the original chord spans an octave or more.
Thus, E-G-C is an inversion of Cmaj (C-E-G), and Csus6 (C-F-G-A) is an inversion of Fadd9 (F-A-C-G).


Any inversion/voicing of a chord which spans at least an octave. That definition applies even if the original chord spans less than an octave.
Thus, E-G-C-E is a voicing of Cmaj (C-E-G), and Fadd9 (F-A-C-G) is a voicing of Csus6 (C-F-G-A).
CHORDS WITH MISSING NOTES ARE NOT VOICINGS OF THE ORIGINAL CHORD! They will be listed in chord choices instead or appearing as inversions/voicings.
I understand certain instruments, like mallets for example, can hardly play more than 4 notes at the same time, hence chords with missing notes tend to be refered to as "voicings" by those who play them,
but as per the strict definition, a voicing of a chord must contain EVERY pitch of the original chord, no missing ones, no added ones, no altered ones. The voicing is how the notes are placed, not what notes are chosen.

I made an exception for 13th chords because of what's explained here and did not include every corresponding 13th chords as voicings of each other.
The reason for this is rather simple : suppose I have a voicing of G13... since as per the definition Cmaj13 is a voicing/inversion of G13, then do I also choose to consider every valid voicing of G13 as a voicing of Cmaj13?

It's that the logic behind entering chord data and making a given chord a voicing of another of multiple others, and especially of assigning what note of the original chord is the root of the inversions, etc, is very intricate and making it as just described would make entering a single chord an hour-long, mind-boggling job... Take a look at the data needed,
and if you can really make sense of how it works, then I may grant you privileges to enter chords by yourself rather than just using the suggest chord form...

In addition to that it will just make the results for 13th chords more readable, and logic. It is widely known and easy to understand that a 7note chord will be a voicing of another chord containing the same scale notes; the answer is given in advance. For chords not containing all the notes of a known scale, however, the mystery remains interesing to unsolve...