Practically all traditions and folk music around the world have been passed down orally from father to son throughout history. This can have certain disadvantages when it comes to knowing how a certain tradition has evolved or how 'pure' it has remained; as well as the history itself, since it is difficult to know since when a tradition has been as it is today.
Verdiales has always been passed down exclusively orally and that is why there is so much uncertainty or so many doubts about its history. It is increasingly possible to make more and more connections and reach conclusions about its relationship to civilisations and cultures of other times, but they are still hypotheses.
Verdiales used to be given in family contexts, so it was common for people to learn from their own parents or grandparents from a very young age. In other cases, some instrumentalists had some young people as apprentices to whom they taught all their knowledge and skills. 

Since a couple of decades ago, everything is much easier thanks to verdiales schools. The teaching is still generally by oral transmission and imitation. However, in some special cases or simply to have the option of remembering the music if you do not play it regularly, there is a method of writing by tablature.
In my case, I keep all the music (in its basic form, without ornaments) written in tablatures. I learned to play verdiales only a year after I started playing the violin (at the age of 9) and my teacher, in order to remember well what I learned in each lesson, began to use this form of notation. Because of my young age and not being able to go regularly to play verdiales, I was more likely to forget certain details and parts of the music if I had nowhere to go to review it.
The idea he had was to designate with numbers from 1 to 4 the different fingers (as fingerings in classical music), and to write those numbers in the different spaces of the pentagram depending on the string to be played: above the first line, E string; first space from the top, A string; and second space from the top, D string. As it has been mentioned before, the G string is never used in verdiales.

In addition, he noted other details such as the bow up or down with an arrow pointing up or down. If, for example, he wrote an arrow down, it meant that, until the next arrow is found, all those notes would be tied in the same bow.