I may also be wrong here too....
There is a limit on how far back you can go. You can wear your grandfathers medals if you were born before his death (and great-, great-great-, providing all intermediaries are deceased)
Otherwise you could have Walts pitching up with Chelmsford 123, Hastings 1066 medals etc.
Anecdotal:
I did once hear of an airman asking the SWO if he could wear his grand-father's medals at a Remembrance Parade. Permission was duly granted, so SAC Schmidt (can you guess it.......)
turned up wearing an Iron Cross.
SWO apoplectic, passing FL300 and climbing!