There's not a straighforward answer to your question. Let me make some
When your husband purchased his ebooks, they were downloaded with certain
digital rights that were set by the publisher and the reseller. Those
rights may have restricted the use of those ebooks to one download to one
machine. That is probably the reason why your husband can't download them
again. One purchase = one download..... However, those digital rights
normally do not prohibit opening and reading the ebooks more than once after
they have been downloaded. After all, you did buy the ebook, not the right
to read it once.
Each reseller/source on the Internet can have different rules about the use
of their ebook downloads. I am sure that downloading ebooks from two
sources should not result in denial of access to previously-downloaded
ebooks from another source, so I'm confused as to why your husband is having
a problem. Nothing that a different source does should affect what's been
done by any other source.
If you can get more information, then you can talk with others about what
the problem really is and what they can do about it. Your husband should
take a look at the digital rights and status information about the ebooks
that aren't accessible and write it down. You do that in ADE by going to
the title of the ebook and pausing your cursor on it. A small arrow will
appear next to the title or cover. Put the cursor on that arrow, and a
drop-down menu will appear. Pick 'Item Info' from that menu, and you'll see
a display of the ebooks information. The middle section will tell you about
digital rights. If they are restrictive, it will show there.
Fixing the problem..... Deleting and reinstalling ADE won't help. It's not
SONY's problem either. KOBO can issue another license and when you download
them again, they "should" work. Tell them what digital rights are showing
for the ebooks in question, so they can cross-check with those that they
know are assigned to the ebooks.
Hope this helps!