Many thanks to the OP again and glad you're not injured.

My 4 regular rides all have the same Nitto short technomic stems pulled out to the max insertion line, then back in a mm or two to be sure. I need them higher as I age and am reluctant to give up on drop bars. Pulled apart bike #1, an 89' Miyata 1000 with the original headset and fork. Measured the threaded portion of the steerer and was surprised to learn the stem wedge isn't fully below the threads. Mostly, but roughly the upper 5MM of the 30mm taken up by the wedge is under the threads. Minimal overlap but I'm seeing comments from venerable posters here saying the wedges must be fully below the threads. I thought I was safe following the minimum insertion line but once disassembled and measured I now know it's simply not enough. I suspect my other bikes from the same era may have the same problem.

Solutions? I had avoided the longer Technomics fearing that other problem where they can go too deep into the butted bottom of the head tube and not engage squarely. This was my main reason for choosing the lighter Technomic short versions. My bikes are 56-58 so maybe there's enough headtube to go deep under the threads without hitting bottom.

Plan B I could insert the stem another 5MM to erase that overlap. Harden up a bit and get lower I guess. But I'd still be on the edge of those threads, thinking about this "thread".

I suspect many on the C & V side being older and maybe less flexible are at minimal insertion on their quill stems. Definitely worth checking. Thanks in advance for your advice-replies.