What's your point in asking why I knew that? You are the one who initially brought up the point about it being clumped together, and I simply was explaining why they might have done that. I'm not sure what you are insinuating.
But to answer your question, I know that because I have an uncle who is a physician and I am interested in medical stuff. Regardless, this doesn't help move the conversation forward and address the original question. To your original question, the main indication for Retinoids are for acne, however, it was inadvertently discovered that they had anti-aging benefits. That is why you see all the cosmetic companies jumping on the bandwagon and offering "Retinol." Of course, they cannot offer the prescription level tretinoin, so they are using a cosmetics grade version of Vitamin A for their over the counter products. The truth is that Retinol is converted to Retinoic Acid (which is Retinoic Acid / Tretinoin), when it is absorbed into the skin, but is many many times less potent than true Retinoic acid.