If you use megameklab, you can find alpha strike stats for a given unit in its preview tab in the AS card subtab.
I don't think there are any errors in how megameklab does the calculations?
The stats, aside from PV, seem to match Solaris SkunkWerks BattleForce calculator. Not having the Compantion, though, I haven't been able to check.
As a note on MegaMek, it's only the last few Development versions which have the AS Card calculator. It IS finicky as to which version of Java you have installed, so...
I've used it for our local campaign when we do Alpha Strike scenarios as we have a a notable majority of Mechs customized for our preferred fighting styles. It's been very nice to have. And combining that with the Alpha Strike Card Generator, I can even put the pilot's name in as well as their SPAs on the card.