Some of us are merely transmitting how astrologers viewed the 12th house for the past 2000 years. We don't have to like it or agree with it. History is what it is, however. We can't deny it.
Nothing is certain except for death, taxes, and AW
I seldom state any "facts" about what what X, Y or Z means in a chart unless I am referring to my own. And unlike many people, I have always made my chart available to anyone who wants to check.
In my chart Pluto does not count for traditionalists, so I will only mention Venus and Saturn.
Here is how it plays out for me:
Saturn in the 12th: Saturn symbolizes the father in a night birth. Dad may have been missing or emotionally unavailable to the child.
We always have to remember that what we are "reading" is about the individual or "native", not about another person. I was born after midnight. My father was invisible to me as a child. He was just a "nice man", distant, and he seemed to take a back seat to my mother. Passive, self-contained, conservative, very fixed. We had no birthtime for him, so I have no AC, and the Moon could have been in Cancer or Leo. That's a huge difference.
Fast forward: before he died my father went into a coma, only for a day or so. We became VERY close. I found out that my "distant" father never judged me, never criticized me, always quietly supported me, and in every way that truly counts was a FRIEND. You don't get more than that in this life. So after becoming so close, I was there to hold his hand, and while I did he slipped away. I'll let other people come to their own conclusions. The lady who was there said that she had seen this before and that he was waiting for me to be there before leaving. I choose to believe that.
POINT: my perceptions colored my dad as distant, when I was young, and his own nature made it impossible for him to change my misconceptions.
relationship planets in the 12th (moon, Venus, Mars): Are we fully conscious of how we behave towards others in relationships? If not, they are apt to be a source of difficulty for us. [from Robert Hand, Horoscope Symbols.]
My take: very few people are more than a very little self-aware, so they tend to be blind to both their strongest and weakest points. The Venus/Saturn conjunction in my chart, about 5 degrees but in different signs, played out this way:
I was a lonely kid. I learned to hide vulnerability, so successfully that I was viewed as arrogant, cold, aloof and conceited. That is what I was projecting. I only knew I felt lonely, not connected to anything. A series of experiences hit me like an avalanche in my late 20s (Saturn transiting 12th, "Saturn return") and my whole life was torn up in my early 30s (transit of my 2nd house).
So was the Venus/Saturn conjunction in the 12th "hidden"? Yes. Totally. The study of astrology was they key that unlocked this mystery. Things that are hidden do not have to STAY hidden. But they have to be looked at first, which is usually very painful while going through the learning experiences.
That's my personal view of my own chart, for what it is worth to other people.