Related Employers - Past Transition period - Different Plan Years

[401kology]

While I am aware that in order to permissively aggregate 401(k) plans that must have the same plan year, same HCE definition and use same testing methods for ADP/ACP, what I am wondering is if anyone has experience in 401(k) plans with different plan years (one runs on a CY basis and the other is a 6/30).  

How is the coverage tested - as a snap shot at each plan year end?

Of course, we found out well beyond the transition period.  And, am referring to outside counsel but for my own edification was curious as to others experience? Like, assuming it fails - how do they correct coverage with QNECs?

TYIA!