What cards were never allowed in Commander?
According to this MTG Salvation forum post, the very first EDH ban list that applied to the very first decks that were played in the format is as follows:

Collector's Edition, &quot;Promotional cards&quot;, poker cards and silver-bordered cards are banned. (I'm assuming poker cards are the 52-card, Magic-backed standard playing-card decks given to early DCI members.)
Unique Portal and Starter cards are banned. (This means Portal and Starter cards that don't share a name with &quot;standard&quot; Magic cards.)
Vintage-illegal cards are banned.
Test of Endurance is banned.

Later in that thread it says that Test of Endurance was unbanned in 2008. I'm not really sure what Portal and Starter cards it's referring to, but no such cards are listed in the current Commander banlist so either they were unbanned at some point or they were never Vintage-legal anyway. Based on the information in this article, it looks like the only cards banned in Vintage at the time were Shahrazad, Chaos Orb, Falling Star, and ante cards.
So, the list of cards that have never had a chance to see play is just the Vintage banlist.