How do you get from four to six research slots for mercenary?

[Fey-Yell]

So I got to reincarnation 75, and unlocked Mercenary Research. I look online for the guide on what research build, and all the builds have six slots for research, and I have only four. I am sure I am missing something, but I don't know where. I have looked over the artifacts, and the change isn't there. The wiki says you begin with 4 slots, and that is what I remember. The secret trophies were supposed to increase each by one, and I remember them doing that (and still doing that for all non-mercenaries.) Only the mercenary builds seem to be off. Was it changed so that Mercenaries now only have four slots each?

I looked around and found one of the general slot upgrades was moved to 90, but that still leaves me shy of 1 each, and I don't know where.

[PseudonymousBosh]

Six-slot merc builds departed from this world some moons ago, and are now merely one of the derelict fandom wiki's many charms. Since those charms do not include reliably current game information, you may prefer G00F's site on musicfamily as your source for builds.