1.1. 3 or 5 serial sample-portion (dilutions)

SMEWW 9221C indicates the use of 3 and 5 sample sample-portion (10, 1, 0.1 ml). As I understand, both are fine. If using 3, you can dilute the sample first and consider the diluted sample as your working sample. Then look up the MPN table and multiply by the dilution factor. So, is it necessary to make 5 serial sample-portion (10, 1, 0.1, 0.01, 0.001 ml)?

1.2. E.coli in EC-MUG and Tryptone

SMEWW 9221F&G describes how to analyze E. coli that has the ability to cut MUG to produce fluorescence under UV light (9221F), and E. coli that does not have that ability (I am doing the indole chromogenic reaction) (9221G). There are strains of E.coli that are capable of cutting MUG and producing indole. Is there any way to choose/calculate into a single value in the test results?