Published in a Tablature Edition for immediate pattern visualization and a Standard Notation Edition for traditional reading.
Unlike standard method books (like Parkening or Noad ), a "compendium" implies an all-in-one encyclopedia. You theoretically do not need another book. This is why the PDF version is so coveted. The Classical Guitar Compendium Pdf
A good compendium will not just show plucking . It will diagram vs. free strokes (tirando) . It should include the "PIMA" notation (Pulgar, Índice, Medio, Anular) with progressive polyphonic exercises. Published in a Tablature Edition for immediate pattern
IMSLP contains thousands of classical guitar scores. You can create your own compendium PDF by downloading individual pieces from the original editions. This is why the PDF version is so coveted
Don't overlook this. A great PDF will explain punteado (plucked) vs. rasgueado (strummed) notation, as well as modern symbols for percussive effects.