Mistakes were made

The downside of having a fair amount of rail material to work with is that it might lead to over-ambitious & ill-informed planing. I did that.  Planed through the rail thickness, exposing a lateral hole along the rail in the middle of the board.  I ended up with 4 patches b/c it took me a bit to understand how to fix the problem. Lesson: the thinness extends much farther than where you broke through so cut a big hole for the patch or you'll be back with more patching. That seems obvious now, but . . .
Patching meant cutting out  thin parts of the rail or deck, filing edges so they are straight as possible, cutting material to fit the hole, gluing, and planing to match surrounding wood.
Using a triangular (or pentagon) profile wood patch, I found I could jam the point of the triangle into the hole and the edges would self-seat neatly against the edge of the hole with pressure - that's far easier than cutting a patch of the exact dimension of the hole.  The length has to be right, but the sides will self-seat with pressure from clamping.  The triangular or pentagon shape, also gives a flat outside surface to place your clamp.
I viewed this as a colossal screw-up, but was happily surprised after planing things down.  The patch is noticeable but you have to look for it. It almost looks like an intended part of the laminate.
Not to dwell on screw-ups but the final patch was particularly embarrassing.  After 3 patches I had the problem solved and things looked good . . . until I lifted and flipped the board and heard debris fall from one side of  to the other. I hadn't shaken it out before epoxying in the patch. It was too embarrassing to leave so I cut the whole thing out plus some, shook out debris, and re-patched.  A dumb-ass mistake. It's a good thing this isn't my day job.