From their discord:
"Here comes the long awaited update!
This should give everyone the well deserved insights on why the sets, Sumi and Stealth, haven't made any progress after the approval of the colors.
With GMK sets, the usual procedure of sets being approved is the following. First the colors will be matched to the desired shade. This step did already took very long, but we are very happy with the final result and the ensured quality that comes with it.
The next step is the confirmation of the Kits. This is necessary to guarantee the correct keys in each kit, as well as the novelties. And that's where we ran into some issues. As I started to design GMK Sumi and GMK Stealth I used a different vector program as GMK did (this changed with Modern Ink, as I switched to Adobe Illustrator). Somehow the shared files for the novelties, which had been sent to GMK prior to the GB, that should ensure the producibility of each new legend had a wrong scaling. This stayed unnoticed until we came to the before mentioned step of checking the kits.
Revisiting the Novelties in order to get the proper scale ended up taking way longer than initially expected. We had some problems to correctly align the enter novelties which ultimately ended up in GMK creating a sheet that took care of the problem. Besides that I had to slightly rework a novelty from Sumi (無), which had tolerances that were too tight for production. This change is only very minor and not noticeable in the grand scheme of the kit, but I still wanted to mention it.
I'm pretty sure that the final result ensured the best Quality of both sets and I'm really looking forward for them to enter the production followed by their delivery!
I've attached the final renders of the Novelty kit from both Sumi and Stealth that came back from GMK.
In order to compensate everyone for the unexpectedly longer waiting time, I decided to add a couple of specifically designed Sumi and Stealth themed Stickers to every order.
With both Sets being in the queue for production, the ETA shouldn't be too far in the future.
I will update everyone, once I know that the production started!"