Thanks all for the suggestions!
Soundaboard offers no evidence for their statement. They probably wrote this based on the note from the original bootlegger.
This recording is likely distinct from the 1977 Mantra Studio live recording (e.g. https://www.ebay.com/itm/Styx-Live-1977-Chicago-CD-Very-Rare-Radio-Broadcast-/373383335269). But I can’t exclude it.
One more bit of information. When introducing “Lady,” Dennis De Young says “One of the first times we ever played this song was right here, on this stage.” “Lady” was released in 1973, which suggests it was performed in the Chicago area, but styxtoury.com does not include a performance at Auditorium Theater in 1972-3. This clue might be possible to resolve with more research.
With all of these considerations, I feel there remains reasonable doubt about the date and venue. Therefore I will go with @jesus2099 suggestion, but describe 1977-09-23: Auditorium Theater, Chicago, IL, USA as a likely candidate in the annotation.
Pre-FM source (why don’t they just say AM?)
LOL. I remember 1977, we didn’t have MP3 yet but we did have FM.