Thanks to all of you for your responses.

I like the idea of pulling and replacing the single bolt to check.

The old bolts, which I still have, turned out to be well within stretch specs. I bought replacements because I knew I wouldn't be able to inspect the originals until it was too late to get new ones. Since I had the new ones, I used them.

My only concern would be removing a single bolt and its possible consequences for the straightness of the head. I suppose it wouldn't be much worse than it already is if that bolt has not been holding proper torque. And if the cinch-down doesn't work I can always check the head when it's off and have it shaved again if need be.

Thanks again to all of you.