If you buy blocks to check your mikes, you can't use your mikes to check the blocks. Unless your mikes have been checked. And if you could do that, you wouldn't have bought the blocks.
You wouldn't measure your height with a ruler and then say, "Let's see if the ruler is right. I'm six feet tall (according to the ruler), so we'll check it against me."
Because steel and other alloys are quite active, they are always on the move, in spite of having been heat treated and cold cycled. Blocks change, and can grow or shrink. One of mine had changed about .00050" from the original calibration to the next calibration.
This appears to bring us back to, "You can't measure to the tenth without paying someone to check your equipment," so we're back where we started.
The clear conclusion seems to be that you have to spend a lot of money or forget about measuring to the tenth. So if you're cheap, the tenths marks on micrometers have to be ignored, and you have to be happy with the nearest half-thousandth.
It sounds like the old caliper argument. People claim their trusted Starretts are accurate to within a thousandth, but they're really just looking at repeatability, or they're squeezing the jaws just right to get the results they want to see. They don't really know how accurate their calipers are.
I guess now I should focus on figuring out how to split a thousandth reliably. As for sizing stuff for press fits, it sort of sounds like emery cloth is the only hope for a cheap machinist.
Every hard-fried egg began life sunny-side up.