I noticed a friend of mine who last played in 2014 has a 
in his game, even though it didn't exist back then. I also noticed brutalizer was replaced on a Riven in a match from 2014 with 
. Are items coded by number in match history and are these codes reused when an item is removed?
http://i.imgur.com/EuDfisP.png
Also wards say "Monster eye"
as an amatuer coder, i can say it is probably the case, if you look at items, wards, champions etc. on server-side you will be looking at some random numbers, that your client know how to de-code and makes it into the thing you know.
long story short, yes items are stored as numbers, and when an item gets removed from the game they just change it with a different one. i assume it's to avoide people who manage to manipulate the system, to get it again.
sry for my english, hope i was clear enough
