Only older version of a word file is available. How can I recover a missing newer version?

There are four basic possibilities - (1) It went somewhere else (in another directory), or (2) It got a different name, or (3) It never saved for some reason, or (4) You accidentally copied the wrong way around (old one from flash drive over new one on hard disk).

(3) means it's gone. (4) means you could try to search with low-level programs through your hard disk for remainders of it, but chances are very low to find anything at all, not to speak of finding a functioning document; especially as you say you did lots of other things. (1) and (2) should be easy; search your complete hard disk for .doc (in Explorer), and sort by last change date.

My recommendation is try that search, and if you don't find it, bite the bullet and start to rewrite it. Anything else cost you many many hours and has very little chance.