My understanding is, we wouldn't have Zirak around in Season 3. We'd introduce him in Season 4, as a young wunderkind jewelsmith. Then, as a very, very venerable dwarf (400-plus), he is the aged voice of peace in the dispute over his necklace.
I agree, the dates don't work, exactly. Corey has suggested that dwarves in First Age can be longer lived than in the Third, that they go through a similar "fading" as elves. We also might condense timelines, again.
This was not my idea, and honestly, I'm not in love with it. I get the impulse to have the creator of the Nauglamir be someone important/famous, and to have a senior dwarf arguing peace to nuance the fight more than it is in published Silm., but I actually think having that be the original maker creates more problems than it solves. If the original maker is right there, saying "hey, it's cool, it's Thingol's", then that makes the other dwarves' position ridiculous.
All that being said, I'm not mortally offended by it, either. I'm not as tied to the absolute chronology as some here seem to be, though I do care about relative chronology. I don't mind condensing, so long as it still makes sense (no teleportation necessary for travel, characters have time to be aware of/digest relevant information, children are not having children to keep the family trees moving...) Furthermore, like I stated above, if we have Telchar established from day 1 we don't really have a role for a mentor/master figure. If we don't have a place for Zirak here, it makes sense to keep the name/idea for something else.
Again, don't love the idea. But I'm not made indignant by it.