"Apple" or the iBookstore support team are not responsible for software not being available - although I dont think it unrealistic to keep older versions of any software available at least for 6 months after upgrades.
This issue seems to demonstratethat the developers of iBA never tried opening "old" products on upgraded software - either that or its another Apple brick wall .. our way or no way!'
BUT
The day before the last iBA upgrade I had delivered a book for review.
Next day I updated iBA, iTP etc and the book would not open ib iBA again. I tried all the delete index page etc suggestions and finally put the problem to support. They went through various fixes..none worked my request was escalated to the the software team ( I think) who asked me to send them the iBA file ( are they crazy!) I dont know any email service which will attach a fie in excess of 200 meg! I replied that I could upload to my server and or Dropbox and send a link.
They supplied FTP info to upload to their server - which I did. About seven days later I had an email with FTP details to download load the iBA file, it had been re-named as a version or the original and when downloaded opening in iBA without issues.
Obviously this saved me hours of work creating an update to replace a defunct file.
I suppose the message is if you have a problem push support for a solution and ASK for your file to be repaired, after all its "their" software glitch which seems to have been missed when "they"- presumably - tested before releasing the update.. then again that also applied to Maps!