Firstly, if:
"It is well documented that The Who played in Boston on 12/3" then they couldn't of been in Philadelphia playing as well.
Secondly, I've had a rumage through my bootlegs and I have 3 vinyls from this gig. Although none of them are date specific I have sheets printed off from the "Baba O'Riley's Bootleg Page" webiste for each record and they all say the date of recording is 12/4 (which was a Tuesday btw).
If it's of any use the 2 tracks used from 12/6 Largo may well be "Pinball Wizard" and "See Me/Feel Me -We're Not Gonna Take It".
So my best guess is the engineers labelled the tapes wrong. Possibly for a laugh, 35 years later! They may well of been labelled up a week later and a simple error was made, easy to do.
*update* - I'm totally confused now, I just checked the 12/6 show on WV and that has Pinball Wizard and See Me Feel Me on it too! The notes I have from "Baba O'Riley's Bootleg Page" say the last two tracks of 12/4 Philly were infact from 12/6 Largo.
I did notice Roger changed the lyrics on Pinball Wizzard (Philly) to "I aint seen anything like him in any COMMUNION HALL" (instead of amusement hall). Maybe this is a clue to where they were if The Spectrum or the Capitol Center is known as a communion hall. Or maybe it's just a English to American-English conversion he did because he felt Americans wouldn't understand 'amusement hall'.
My head hurts, has anybody asked Pete?