Hi wheresmykeys.
I'm no expert but here's my shilling's worth:
during an eeg the technician will ask you to "close your eyes", "open your eyes", "breath deaply" etc etc..
Afterwards, when the neuro looks at the eeg print-out he/she should be able to spot any unusual activity that took place during the session.
From simply looking at your eeg report (without knowledge of your medical history) there is no way of knowing if the abnormal activity was there 1 month or 1 year ago.
Your historical data is known only by you and your neurologist.
Dunno where you're from, but usually that's all very confidential stuff.
From just looking at an eeg report it would be presumptious to say he/she has had epilepsy for x amount of months/years.
If however, you go for a cat or mri scan it is quite normal to make certain assumptions.
Let's say the imagery shows substantial scarring then it would be obvious that the scarring didn't appear overnight. Bar an accident fo sorts. Hence the symptoms of epilepsy could have been obvious for some time.
But even then, it is possible that the patient never experienced anything strange.
I hope you find you keys.
:-)