Yeah, I'm pretty sure the latest update for Optifine and the other mods are using an older version of Forge 1.13.2, as the update time showing on the websites are in February of this year. If I'm unable to get a version at or prior to their update date, I'll just have to wait for Forge to be out of beta with 1.13.2 and they update that.
Also, the 1.6.4 is the version of the mod, not the version of minecraft, which is a bit weird and misleading to put imo.
Thanks for the reply, too, I just wanted to be sure I'm not missing something lol.