Wikipedia reports red M&Ms were eliminated in 1976, and added back in 1987. I'm sure it took several months for these changes to make it to the marketplace, but probably not years; M&Ms have a reasonable shelf life, but they do degrade, so year old stock isn't great.
My Mom was pretty salty about the red M&Ms going missing, and refused to eat blue M&Ms for quite some time.
As I said, I’m pretty sure that number is wrong by a little. And does 76 mean January or December? That’s a long time for small children. This thread is about people announcing things and then taking a while to do them. But we were in a town hit particularly hard by a recession. I have no doubt they were turning inventory closer to the Best By date than yours was. I bet all those sales I remembered seeing (3 for a dollar!) were overstock.
My Mom was pretty salty about the red M&Ms going missing, and refused to eat blue M&Ms for quite some time.