That was his plan around the time of writing Grundrisse. He later compacted it to a 4 volume plan, with some planned bits for each of the volumes in the original plan being combined into each other or getting dropped entirely because there was no point in Marx writing about it. The first volume from this final plan was published during his lifetime. The manuscripts for the 2nd and 3rd volumes were edited by Engels after Marx's death and published. After Engels' death, all of the manuscripts and notebooks were inherited by the Second International, and Karl Kautsky working for them prepared and edited and published the research notes and manuscripts for the final volume in a 3-volume series as Theories of Surplus-Value [Theorien über den Mehrwert].
It's also why the final volumes are so thicc. The different sections in them were meant to be separate books of their own.
A mailing list was set up in the 90s for that purpose by Allin Cottrell and friends and immediately got derailed into all sorts of Marxish topics. Andrew Kliman was also there and threatened some critic with assrape IIRC.
they didn't finish because they're pseuds
False. They didn't even have a proper start. They were the most intelligent Marxists, completely dwarfing anybody marxblogging or marxpodcasting today.