Sometimes a book is printed as a hard cover and a paperback. Each version can have a different ISBN. Sometimes both versions are listed in print copies, I believe the (pbk) is in print to show the difference. I don't believe there is anything that covers this in any of the manuals, but I have never seen the pbk included in a brailled version.
For questions about manuscripts it may be best to send a question to Jennifer Dunnam at the National Federation of The Blind.