Help! Where's 'ignore all' and 'Add to dictionary'?

Well, if it does not happen to new documents, then it sounds like some sort of file structure issue. Try Selecting the whole document EXCEPT the very last paragraph mark. Paste it into a new blank document you created. Save it.

If the mass copy does not work, (I'm guessing it is 3-400 pages long) and you have the patience, try copying it in smaller groups of pages, say 50 at a time.  Again, make sure to avoid copying the very last paragraph mark.

Rather than "upgrading to 2013" just to fix error in an older installation, unless you also have other reasons for doing it, you probably would have been better served to have done a clean uninstall of 2007 (using the fix it tool) then re-installing it.  There is a good chance that would have cleaned up your issues.  But too late for that now ... unless you want to upgrade back to 2007.

PS: it was Word 2007 or Word version 12, and Office 2013 or Office version 15. If you call 2013 Office 13 you will be making a bunch of MS marketing people cry. <grin>

Earlier (before 2013) versions of Word do grammar checking and one of the options is to tell it to ignore one of the predefined grammar rules, like single or double spaces after a period at the end of a sentence.

I do read a lot of sci-fi, I just am a "traditionalist", I prefer hardcover or paperback books (and I'm cash too short, and cheap <grin> , right now to buy an ebook reader ).

I know it's a long shot, is there any chance you are related to the 1950's British sci-fi writer Jack Williamson, dad or grandfather?  I have a few of his books in my library.