In previous records TSMC improves yield very quickly so I don't really concern.Yep usually devbox have get the silicon lottery of the chips. Xb1x devkits had 44CU / 44CU enabled chips.
If the cream of the crop chips selected for PS5 has only 77% of its CUs active, then AMD/TSMC fucked up, because it's about 6 months away from full production...
Also when was the last time a GPU had over 23% of its CUs deactivated haha.
One more possibility is that SONY doesn't want to show how many real TFs they may have.
So they deliberately only activate 40CUs even they can activate some more CUs.