For example, grimlocks drop standard coins, standard goods (gems only), and standard items. What does it mean by "(gems only)"? So far my guess is that I roll normally, but if the result is some art, then there's neither art NOR gems to be found.
Some entries for goods or items include notes that limit the types of treasure a creature collects.
When a note includes the word “no,” it means the creature does not collect or cannot keep that thing. If a random roll generates such a result, treat the result as “none” instead.
When a note includes the word “only,” the creature goes out of its way to collect treasure of the indicated type. Treat all results from that column as the indicated type of treasure.
It’s sometimes necessary to reroll until the right sort of item appears.
Normally you would roll d100 to see what type of goods you have found. Instead of that, you only roll for the number of gems, and a d100 for every gem to determine what kind of gem it is.
A grimlock with 4 levels of warrior will roll a d100 to determine the number of coins and another d100 for items. For gems you will only roll a d4, because the CR is 5.