If I am to hold the original plat bearings (all of them) and call out at least two state plane coordinates on opposite corners. I am slightly disagreeing with the plat bearings even though they say they are on the same datum I am using. So I hold them and its easy enough to call out 1 SPC and slap one of the corners onto that one, right. well either I go by the meets and bounds of said plat (lets leave out grid/ground) and put a SPC there that I think would be the wrong coordinate or do I put the right coordinate on the opposite corner even though the math would not work out?
What do you guys do?
I always like to report my actual findings.
When required, which is most of the time, I also show the called information.
As my past experience have shown, when you find one thing and the called information is within state tolerances of what you have found, both are usable.
Go figure and use wisely.
😉
If some requirement tells you to call out the SPC's for two points, I would call out those state plane coordinates exactly with not rotation, or multiplier (I don't know your elevation or what kind of distance error that might cause either.)
All you might do is call out a rotational value to go from your bearing base to the state plane bearing base at one point. That might cover your butt for someone who doesn't understand state plane.
When a client requests a project to be on SPC, I have in the past supplied SPC on several control points, but also have supplied "Project Coordinates" on those same control points so the next guy in the field on the project will have "ground coordinates" to work off of. I know this isn't exactly the same thing you are facing, but you may be able to do something similar.
It sounds like you calibrated your GPS survey to at least one good line of your record boundary. Maybe a couple other points and then pretend to adjust them. I do that all the time so that I can hold the record bearing basis and not mess up lawyer & title company types. But prefer to just hold the "best" line and rotate around that. Typically on an assumed 10K, 10K datum. Show discrepancies as "record & measure"
Now somebody wants SPC. No biggy. Show the SPC on a couple points and let them figure out your rotation/translation. You'll likely get more work out of it.