Margin mirror problem in Word 365 and Word 2010

[Luther]

I have searched with Google and in this forum for a solution and nothing seems to work. I have published several books using Word for Windows with no issues. However, a recent book will not properly mirror the margins. Since I have it right in the others and since all the settings appear to be the same, I am at a loss as to why the recent book will not properly mirror the margins.

The new book was derived from a prior one...shortened to create an abridged version. Consequently, there has been considerable cutting and pasting to make sure the comparable texts are the same. This is fundamentally the only difference in the process for writing the shorter book, which is the one with the margin mirroring issue. It is the outside margin that is the issue. The inner margin mirrors.

I am totally stalled, since none of the suggestions I have read seems to work. Any help would be appreciated.