Indeed, otherwise there'll be a number of pilots sitting around twiddling their thumbs & looking for a ride...
So, I guess it's a fair assumption.
Actually, re reading it, I think it may be a typo & you were probably correct anyway. Why would a service life of 18-20 years be an "extension"? If they were leased or something, then perhaps it could mean extending their time in RAAF service rather than life extensions...
This is why I sit behind a desk!