Hi SK
Ideally if you are on the latest SP's , then this wage type /3I9 should be present. Not sure why its missing or something happened during any upgrades.
I would again request you to check the same in your client 000 of any of your development or test systems whether the wt is there or not.
Also you can check if other changes gone via 2168787 are present or not ? as per the manual attachment.
If only /3I9 is missing, then you need to check in client 000 and the same should be transported from there itself.
Take the help of basis people.
Regards
Chetan