which raises the question, how did Ford learn this information?

Option 1 Ford heard other people singing a three part harmony near a z-boi or

Option 2 Ford himself was in a three part harmony

Which raises a follow-up question, who was Ford signing a three part harmony with? I mean, Fiddleford was probably one of them (if the timeline adds up that is), but that still leaves a mysterious third singer, It couldn't have been Bill because he was still trapped in the nightmare realm. Maybe it was manly Dan? Or lazy Susan? Or Stan

All that to say, I sketched/redrew a frame of Scary-Oke with the mystery trio

I actually found the cannon answer in the special edition of journal 3