Alright so i'm in need of some advice. Currently I acquired both Nemesis and Slave weapons for my main class in preparation for the NT Zeig weapons we will be getting eventually.

So from what I understand, the Austere-NT weapons require the NT versions of Nemesis and Slave (And a few others we currently do not have) to be grinded to +35 and then traded in for the 15 star Austere-NT weapon. You can exchange Nemesis and Slave weapons at Zieg for the NT versions of them and they come with the same grind level you exchanged them at. (Ie if you trade in a Nemesis +23 you will get a Nemesis-NT+23 in exchange)

So my question is, would it be better to grind the weapons to 35 before exchanging them for their NT versions? Or get the NT versions first and THEN grind them to +35?

The versions of Nemesis and Slave (and in fact every weapon) in the NA version already are the NT versions, as OT weapons are not in this version (save for some CM-only ones).

NT is the designation of weapons that use the EXP system and can be leveled up to +35. OT weapons were enhanced similarly to Units, up to +10 with chances of failure, then unlocking the Potential dropped it back to +0, and needing to repeat the process 4 times total (3 times to unlock full potential, then once more to get back to +10).

@AndrlCh Ah I see, thank you for clarifying, been a huge help.