I find this question interesting but because of my lack of knowledge in music this is a hard topic to solve. However as a programmer with many decades of experience working with symbolic programing languages this has a lot of connectivity to many problems in my experience pool.
Here is another post of similar nature Is it possible to teach ChatGPT to write/draw knitting machine code where I assisted.
The link to the Caeciliae Tutorial is helpful but for GBAC this is what I leaned from ChatGPT.
In the context of sheet music what does GBAC mean?
In the context of sheet music notation, GBAC does not have a standard meaning or usage. It is possible that you may be referring to a specific notation or symbol used in a particular piece of sheet music, in which case more context would be needed to provide an accurate answer.
However, in the context of music theory, the acronym “G-B-A-C” may refer to the names of the notes on the lines of the treble clef staff, from bottom to top, which are G, B, D, and F respectively. This is a helpful mnemonic device to remember the notes on the treble clef staff.
Is that correct? Remember that I know symbolic programming not music.
Also it would help if you showed some conversion examples in your first post (e.g. few shot examples), you should be able to edit that post before the windows closes on editing.