Were adoptive parents ever specifically advised NOT to tell their kids they were adopted? Or was it just Not Done?

There’s no doubt in my mind that it’s a quadfecta.

Here’s something I wrote almost a year ago in another post. It gives just one example about how shameful being a single mother was at one time, and well within living memory:

Edit: I hope I remembered correctly that the airline in question was Pan Am, and not some other well-known American airline.