I numbered the chapters in succession when I wrote the book, and since the 11th chapter was long I divided it into two parts, 11a and 11b. But the title of that chapter was 'Interlude', since it was a transition between Afghanistan and the US.
Which made the chapter I uploaded today the 12th in that sequence.
So if the one you're reading has a heading reading 'Chapter 11' and also 'Chapter 12', don't worry about it. I'll renumber future chapters as I upload them to match SOL's numbers.