Apple states in Note 3 that there were no customers that individually represented 10% or more of the total trade receivables as of both September 25, 2021, and September 26, 2020. Why might information about credit concentration be of interest to investors? Also in Note 3, Apple identifies a certain category of customers that accounted for 42% of its trade receivables as of September 25, 2021. What is that category of customers, and why might this information be of interest to investors?