Actually, Rich, you can't put an exact date on when something becomes a word, especially as since spoken language is perpetually evolving, you have vernacular usage long before a word ever reaches the dictionaries, or indeed written records. This presents an almost insurmountable problem for lexicographers, since tracing the actual roots of a word accurately is often impossible.
I suspect the colloquial use of finalise (and by extension finalisation), as variants of the transitive verb finalize, occurred long before you say, but the only traceable etymology was from 1600s.
Of course, mission2java_78 is also technically incorrect in asking a question that assumes something only 'becomes' a word - and is thus linguistically viable - from the date of the earliest recorded useage.
Although I'm curious now. Where did you get that date?
