It's dated even before use in the office (4,8)

'use in the office' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'it's dated even before' is the wordplay.
I cannot really see how this works, but
'it's' could be 'es' ('e' can mean 'electronic' which is similar to 'IT') and 'es' is found in the answer.
'before' could be 'e' (I've seen this in other clues) and 'e' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?