I have long believed that the "Libro verde" would be a great source of information. I want to share my recent experience with a Libro verde.
I found some information on a line that I am researching and felt that I had hit a jackpot. When I got to the end I was disappointed because the information in the book was different than information that I had. I became very disappointed and did not sleep well that night because if the Libro verde was correct, than a lot of the research that I have been doing was for naught since it stated that the couple that I was researching did not have any children. I did notice a little mistake in the records where they stated that the wife was illegitimate. I knew for sure that this was a mistake since it was a well known fact that she was born legitimate, so I started to have hope that if they made a little mistake, than maybe they made another and my research would still be useful. The next morning, with only a little hope, I returned the Libro Verde and realized that on the far right side was an additional comment stating that it was in error and that the people that I was researching had children. I continued my research into this family and realized that some of the other information that they laid out was not true since I had seen some primary sources on the family.
It was only after this that I then researched the accuracy of the Libro Verde. It turns out that this Libro Verde is well known for its mistakes and that other Libro verde versions do not have the same information. It also turns out that the sources for many of the family trees in the Libro Verdes were documents that we can ourselves pull and should check for accuracy. I took an even closer look at this Libro verde and found many other mistakes on the family that I am researching.
Before using information from a Libro verde, it would be wise to check on its reputation for accuracy.