The specs should be very much the same since .22LR match ammo is made to meet the same CIP ammo specs.
The .22LR match ammo makers don't reveal to the public how match ammo is graded. As a result much of what follows is speculation.
A single production run of match ammo produces a quantity of product which is subdivided into lots. In the case of Lapua all grades of standard rifle ammo result from a production run -- X-Act, Midas +, and Center X. A production run is made by a single loading machine and Lapua, for example, has three or four loading machines (perhaps a fifth by now). No two loading machine produce identically numbered lots.
Lots are identified by a number of factors including certain changes or adjustments to the loading machine, perhaps also by changes in key technical machine operators.
Since all the components of the product are themselves graded -- the brass casings, the bullets, the powder (propellant), and the priming compound -- this grading is very likely serving the purpose of allowing the loading of the best components together, that is using the best graded brass with the best graded bullets (and propellant and priming compound, however that is determined). It makes sense that the grading of components has a role in determining lots.
It seems reasonable that with many decades of match ammo production experience behind them, the match ammo makers have a good expectation of what their production runs ought to be producing. In other words, it seems likely that they know what they will be getting when the production. Perhaps they do some testing along the way to confirm that things are as they should be.
To be sure, things don't always work out as they should. Human involvement and countless moving parts don't always make things as they should be. This may be why sometimes some X-Act is outperformed by some Midas and some CX.
The alternative, of course, is that each day, with each production run, the ammo makers look at the product -- perhaps dozens of cases, tens of thousands of rounds -- and say "We don't know what we've made. Hopefully it's good. Let's start shooting to test this stuff to find out. If it's really good it's X-Act, if it's very good it's Midas, or if it's just good it's Center X. Let's get started, we have another production run this afternoon."
This alternative, that testing by shooting alone determines the grade assigned to a lot, doesn't explain how sometimes a lot that is graded as top tier like X-Act can perform more poorly than Center X.
This is an especially important problem, especially since the factory testing barrels don't magically turn a poorly performing lot of X-Act (or CX) into a good one. Good ammo shoots well in good barrels.
