This is a long explanation (with a question at the end), but I hope it might help some struggling students.
I'm embarrassed that I always shunned reading music. I first learned music a lifetime ago by faking clarinet in band and playing by ear. Then it continued with all the other instruments I learned to play. I always understood the mnemonics for lines and spaces (Every Good Boy... etc.) and understood note and rest duration, so I knew that much, but learning the notes on the clefs was my problem. Many times I tried to study to play the piano the right way and always ran into obstacles in books, such as:
Different mnemonics imply that the F clef and G clef are different (and then they confuse it more by mentioning other clefs such as C clef, alto and tenor clefs, etc.) If someone gets to know the lines and spaces on the treble clef first (like I did), then they find that the bass clef lines and spaces are shifted by two notes compared to the treble clef. That especially seemed confusing when the accidentals of key signatures have to be shifted two places as well between the clefs.
The mnemonics are quite helpful but are words or sentences sequencing in one direction (up) and don't work in reverse (down), and reciting the alphabet backwards is awkward for me (not easy like with numbers). Mnemonics also list the lines and spaces separately from each other and they skip every other key on the keyboard which doesn't make any musical sense.
Another problem is that the pitch of notes on the staff is in the vertical plane, whereas keys on the piano are placed in the horizontal plane. You have to keep track of two different planes among a multitude of other things while trying to play the keyboard to written music. Playing by ear eliminates that problem and may be part of the reason I chose to play only by ear instead of learning to read music.
Well, yesterday I read a small comment in a post here that the grand staff lines and spaces are a map of the diatonic keys on a piano. I found another comment suggesting thinking of the grand staff being symmetrical around middle C. I hadn't really known to think about those two aspects before and therefore never focused on them (though they are very obvious now). Reading those made quite an impression on me so I tried two new things:
I thought of the grand staff as a vertical axis continuum with the direction toward the bass being a mirror image of the treble direction. I contrasted that with a number line and somehow thought about using absolute values.
I looked at the interval distance between the C key and the E above it (a third). Then I saw that a sort of inverted form of that is the A key (a sixth) below C. I remembered that the intervals are diatonic only (not involving black keys). I noticed that the E key above C and the A key below C both ended up equidistant from grand staff middle C, and on mirrored spaces. My concept also worked with F key above and G key below C, and naturally with the octaves (and double octaves).
That's when the mirror image became clear to me and the crazy 2-note offset of the bass clef disappeared. It was a revelation how just those simple conceptual changes eliminated all of the obstacles hampering me!
My question is to ask if the problems I mentioned are solved with the mirroring concept that I explained, and is it taught anywhere in addition to the mnemonic system I mentioned (which is all that I've ever heard of or found in books). [edit:] Also, my intention for this post is only regarding learning the lines and spaces on the grand staff, not learning fingerings of piano or other instruments.