Book order by title isn't working out for me, since for some odd reason 10 comes after 1
In Example: My node titles are numbered from 1- (xx)

Title order should be like this:
1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 . 11 . 12 . 13 . 14

But it's ordering like this:
1 . 10 . 11 . 12 . 13 . 14 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9

I am confused. I do not like how they are ordering, so I decided maybe ordering by date posted or n.id would solve the problem. So here I am asking for your help. I am using the Book-Navigation system under each child pages.

Ordering by weight solves the problem... but I have over 5k+ nodes, and it is not essential to order them manually.

Comments

The ordering using titles is unusual because, in alphanumeric characters, "19." is smaller than "2." etc. This has nothing to do with Backdrop.

I'm not sure I understand your question. Why can't you sort by node IDs or posted date? 

AFAIK there is no option to customise the sorting of book pages: