So there would the be some defective CCDs included.
But low end SKU generally include working parts gimped to match demand for various product segments. AMD isn't planning to do that for the 5600X3D for some reason.
The yields for TSMC 7nm were already amazing when Zen 3 first launched. I don't recall the exact figures, but something like 97% or better yield. If the node has continued to mature, it wouldn't be too surprising for the yield to be even better by now.
Of the defective dies, some can no doubt be salvaged by turning off a core, but others will be junk due to a defect in something that doesn't have redundancy.
Most of the time you get a six core chiplet it's because it can't hit specific clock speeds on all of the cores at the desired voltages. With v-cache the clock speeds aren't going to be as high anyways and so the number of dies that couldn't make the cut would be a lot lower.
If AMD were using only dies that had an actually defective core, it's not surprising that it took them a while to stockpile enough to do even a special launch like this.