What does this even mean? That you invested the only money you ever invested entirely in the relatively brief period of the dot com peak? Who does that? (Obviously not nobody, but ...)

To all effects and purposes, nobody does that. So what it really means is "the money you invested during that one period (perhaps a year or so), and likely only the money you invested in dot com and adjacent stocks, has yet to be made back". In the meantime, the other money you invested before and after the dot com peak has done rather well, unless you specifically made some particularly disastrous choices.