Second Opinion on Series Numbering

[Myndi]

While adding "Angel Private Eye" to the Earthbound Angels series, I noticed that there are several "book 1" listed within the series due to volumes being used. Should the book numbering say book 1 for all 4 of them? Or should it be 1.1, 1.2, 1.3 and so on?

[Renske]

If a book is split in multiple parts something like 'book 1, part 1 of 4' is the best way to number them.
1.1 should be used for a novella/short story after book 1.

[Myndi]

Ok thank you so much!