In a lot of Paganini's violin compositions, there are bolded but sometimes not bolded capital letters like A, B, and C. I look at the note that it is above and it doesn't click for me. In Nel cor piu non mi sento (1st variation), there is a marking, "A1" below the staff and under the note g-sharp, which I really don't understand. Somewhere along the ways of many compositions there is a Roman numeral with a lowercase letter, sometimes with a dot underneath that letter, below the staff. I know that the numeral means the string but what is that letter next to it for? These are really advanced markings I'd assume and I couldn't find what they are in music dictionaries and such, so I'd like to know what all these symbols mean.
Excerpt from score published by B. Schott & Söhne, 1829
Excerpt from score published by Schott, 1909
Excerpt from score published by Editio Musica Budapest, 1968
Excerpt from score of 24 Caprices, op.1, publisher unknown