Sorry, but I don't see anything so far that would indicate why you're having trouble with those files.
iBooks Author has a 'Share' menu that includes the option to email to another user, but that is for .ibooks files, not .iBA.
I'd guess your issue is either related to permissions and/or corrupted files. Perhaps you can take the USB drive into the nearest Apple Store and ask for help trying to understand the issue there.
The file in usb is definitely damaged because it is 200 MB compared to around 1 GB it should be.
When I worked with the MacBook directly on usb I think that once the file is damaged during the last save (I did not realize this before).
In iMac I overwrite the original file with that of USB. Result: I have two files of about 200 MB (one in usb and one in iMac) that do not open.
Now I have only an older version that opens but I lack the important text that I wrote later. I retrieved other files previous Iba with the software diskdrill including one from a GB or so and very recently (4 days before) but it does not open.
I'm interested to recover all the possible text from the file iba that I have.
I know the possibility to send at someone to Apple the file groped for a recovery or at least extrapolation of data (I am interested only written texts).
Can you give me please an email to send the file (I send the link to download it)?
Thank you very much!