The process of gathering the film reels and scanning them to 4K files is probably an ongoing process that will take years to complete. We're talking about 25,000 reels of film. The fastest 4K full aperture scanner can run at 15 frames per second. An average 2,000 foot reel of film has 31,680 frames. So that would take about 35.2 minutes per reel. Multiply that by 25,000 and it comes out to about 611 days non-stop just to scan the film. So, one year and nine months --
nearly 2 years! So, yeah... it's going to be longer than that.
Meanwhile, the editors cut the episodes back together without VFX, then they hand it over to the compositors and VFX artists. They're probably working on a few episodes at a time, at various stages of completion. At some point the scanning process will come to an end, probably when they have nearly half of the seasons out on Blu-ray... and they'll continue to complete the VFX for the seasons and episodes that are left.