You don't use a micrometer for measuring rear spacing - or for measuring anything else more than maybe an inch in thickness. Even vernier calipers will not go up to that width on newer bikes. All you need is a ruler with metric graduations. And yes it could be as you measured - someone could have cold set it to other than the original spec.

Chainline - All you are doing is figuring how far out from the center of the frame the rear cog and front chainwheel are, and trying to make those two measurments the same. You change those figures with different equipment or by moving/adding/subtracting spacers, but the rear triangle has to be the right width for the hub you use and it has to be centered on the frame. That is at least half a dozen variables, and if you are that confused it is doubtful you will end up doing it correctly.

My final word on this: You STILL do not have all the info you need to get proper chainline and cranks, you do not understand BB/crank specs and their interrelationship (let alone the proper terminology), and it is NOT a good idea to get a bb first and then find cranks to "fit." The only way you can predict chainline on the front is by buying a full unit that has that info available or by actually mounting and measuring something you plan to use, and the only way you can tell if the front chainline will work with the rear is to have a cog mounted on the rear wheel, on a properly spaced and centered rear triangle and then measuring and calculating properly.

These forums are wonderful but you have to remember you usually know precious little about who is giving you advice, and you need to do as much research as you can so that you can present solvable problems and properly convey what you need. Your problem is especially hard to address remotely. What is your objection or difficulty in getting advice/help from a bike shop? You could also see if there's a bike club whose members could help you.