The actual point of that, though, is that it's best that you have something submitted on the 30th, but there will be so much subsequent back-and-forth between efabless and SkyWater that if you make changes and update the GDS in your repository after the deadline, those changes will make it on the shuttle. This is pretty much standard practice with all tapeouts. However, I cannot say just how late corrections might be and still make it onto the shuttle.