If you register at EDSM and upload your journals, it will provide you with a number of "systems discovered first". However, that is first with respect to providing the information to EDSM, not first as in being paid the first discovery bonus. I think that there is a statistic somewhere that EDSM has only about 1/4 of the number of systems tracked (>40 million!) compared to the total number of visited systems that FD recently stated.
For the value you are looking for, see the top right in the screenshot. As said, it includes some systems that had previously been visited by other that are not tracked by EDSM, and also the systems for which I have not yet sold the data (>2000 on the current 2 months trip to Colonia - that's where the 3 billion estimated value are coming from

). At the same time it is lacking some systems from the early days after release, for which I don't have the journal files anymore. Like the game today reports that I have done 6371 jumps, but in EDSM I have only 5502 tracked. Though most of those missing jumps have been in the bubble, so... In-game (and also extracted to EDSM) we also have the "Systems visited" stat, currently 5345 for me, but that obviously includes all the bubble systems, Pleiades, … I visited...