The Old Bay Road/Midnight Rock

So I've always been really interested in the early history of ACDC, and these two tunes are especially interesting IMO. You will encounter them on like a dozen setlists from the very early days of the band, but after a couple of gigs they never show up again. I've done some research on these two songs and all I could find was random people claiming they were instrumentals or very early variants of later songs.

My question is, is there any credible information on these songs? Since they show up on fully-fledged setlists I assume there are people who know quite a bit about the earliest ACDC concerts (otherwise the setlists wouldn't exist), but why is there absolutely no credible information on these two songs? Does anyone know ANYTHING about them? Were they genuinely just precursors to later tracks or instrumentals? Also, does anyone know what might have inspired the title "The Old Bay Road"?