Art of Rasgueado by Ioannis Anastassakis is an 80 page book published by Mel Bay. It purports to include all the commonly used rasgueado patterns in the world of flamenco guitar. The listing is, to me, surprisingly small. I have used and seen others use patterns not included here. The introductory points of the book are excellent and clarify that flamenco is not traditionally clarified in terms of pedagogy and most guitarists had to figure out their own ways to accomplish things. Therefore, there are many variations that achieve the same musical effect.
Instead of focusing on potential rasgueados or on the theory and concept of them, this book primarily discusses specific patterns known to be used by professional players, often with specific credit to the player who uses a particular pattern. With each pattern taking at least a page, sometimes two or three, we are dealing with less than a couple dozen total patterns in this book. There are some weird issues that are common to flamenco books, such as including the open 6th string in notation and tablature even though the text says clearly to rest the thumb on that string the entire time.
I would summarize the situation broadly as: each finger, including the thumb, can strum up and down and any pattern that is feasible may be used. Often, a three-movement pattern may be played in a four-note rhythmic situation or vice versa, so the pattern isn't always tied to the rhythm although simple pairings are common as well. It is interesting to note that any back-of-nail stroke is more typical for accents, thus up-stroke thumb is more commonly on the beat than downstroke, in contrast to traditional American folk guitar strumming. The issue for classical guitarists is to recognize the difference between a rhythmically imprecise rasgueado ornament versus a rhythmically specific strum pattern. This is basically all you need to know, and unless you want to know exactly what certain flamenco guitarists are doing, you don't necessarily need this book now.
In conclusion, this fine but short book describes this one aspect of guitar as it is, not necessarily as it could or should be. The attitudes presented are fine, however, and the layout is clear and it is generally well done, aside from a couple typos (one wrong note, one wrong up instead of down marking).