Currently all the entries in the jumpbar (A-Z letters or years) are always available, even if the corresponding entries in the main view are not displayed (because they don't exist or are filtered out).
For example, if the main view is sorted by artists, and no artists in the main view begin with the 'm' or 'n' letters, yet these letters are still usable in the jumpbar. Clicking on 'm' or 'n' will jump to the next artist available in the main view, so for example an artist that begins with the letter 'o'.
When we click on a letter in the jumpbar we expect to jump to an entry with this letter and not to another letter, so the current behavior lacks of predictability / accuracy.
So it would be nice if all the letters currently not available in the main view could be greyed out and disabled in the jumpbar. That is, the availability of the letters in the jumpbar would adjust in 'real time" depending of the current entries in the main view. The jumpbar would inform accurately of what is available and what is not in the main view at the moment, and would only allow to jump to available entries, which seems after all very logical. Thus the jumpbar would be accurate, handier, and faster to use.
And I think this could be also very helpful in conjunction with the jumpbar option 'Enable multi caracters search'. After each new character selected in the jumpbar the remaining characters available in the jumpbar would narrow depending of the matching content in the main view. So a kind of input assistant. It could be very efficient.