Yeah, it's stupid not to include it. Sometimes you can guess it (poorly) by looking at the references, if there is more than a few. If the latest one is at 1998

Yeah, it's stupid not to include it. Sometimes you can guess it (poorly) by looking at the references, if there is more than a few. If the latest one is at 1998, you can guess the paper is from somewhere around 2-5 years after. In this particular case, latest publish reference is at 1998 and one marked as "to be published" at 2000 so that makes it a bit easier to guess pretty exactly :)