In book section, there are many existing fields that I see unused by records in my library.
Book section has already Volume (generic “Volume”), Series Volume (generic “Number”) and Chapter (generic “Section”) as examples. I do see a couple examples that use the Chapter and “Series Volume” fields but would need to look at the originals to see how they are being used and what they represent. Then you need to make the call which one to use, and adjust the Bibliography template appropriately for what you decide. It is clear databases and others use the fields differently.