I'm using the third edition of the Basic English Grammar book and in chart 14-2, it is mentioned that they are as many as 18 adjective categories but the book doesn't go that far as to mention all the categories.
Hello, Ceci, and welcome to the Grammar Exchange!
I'm using the fourth edition of the Azar books, and the fourth edition of Basic English Grammar does not mention that in chart 14-2. It seems to have been edited out, perhaps because it was leading to questions like yours here.
The categories of adjectives are not absolutes. Different grammarians will categorize adjectives in different ways, depending on the reasons for making the categorizations and on their own inclination.
I can assure you that the statement you've asked about is NOT to be interpreted as implying that a noun can be cumulatively modified by a string of 18 adjectives, each belonging to a differently hierarchized grammatical category.