I think people are too quick to assume Marty McFly's parents are completely clueless about the identity of Calvin Marty Klein.
George is a sci fi author who completely bought the idea that a space alien was going to melt his brain. And Lorraine was laser focused on Marty for just about the entire week.
Lorraine in the first timeline remembered the story of how she and George met, and I'm sure Calvin would have made it into the retelling in the second timeline.
I can imagine it going something like this.
Lorraine: "You know I've been thinking about Calvin Klein, and I've come to a conclusion about him."
Lorraine: "You go first."
Lorraine: "Ok, we'll do it at the same time."
George: "Calvin Klein was our son Marty traveling back in time and--"
Lorraine: "Calvin Klein was gay"
Lorraine: "Wait what?"
George: "Wait what?"
And George explains his theory and Lorraine's like. What the fuck obviously that's not true and if it was that would be so fucked up.
He's like "Star Trek and Star Wars were still 11 and 22 years away! But I am sure he called himself Darth Vader from Vulcan!"
But his story makes too much sense. And one day they get in an argument with someone else about Johnny B. Goode. "No it couldn't have come out in '58. The dance was our senior year, that woulda been 1955, and Calvin said it was an oldie then."
One day Lorraine is picking up underwear for her kids on some shopping trip and she leans over to George and says "hah! Look! Purple underwear. Wait a minute."
And they can't say anything to Marty cuz he's just this kid, still too young to be Calvin. And while George is anxious to get his theory confirmed, Lorraine is just trying to keep it out of her mind.
But one day Marty starts acting weird. He keeps getting confused about basic facts of his and his parent's life. And one day Lorraine starts telling the story of how she and George met again and Marty just kinda shifts and fidgets awkwardly and stares off into the distance and Lorraine's just thinking oh my GOD my husband better not be right about this.
But yeah I think the only reason it doesn't come up is we only see Marty's parents for a few moments and they probably don't think of this mystery all that often. But I think they know or at least that it's one hypothesis on their radar.
I do like to think that A Match Made In Space has a dedication to Calvin Marty Klein.