When did a merger really happen

Merger documents says Plan B merged into Plan A as of 12/1st 2024.  The money from Plan B's provider was wired over to Plan A on January 15th.

A) My personal "best" interpretation here is that Plan B no longer exists on 12/1/2024.  The merger agreements say that Plan B is now a part of Plan A.  To me that means the money held by the Plan B provider is now a part of Plan A. 

B) The other interpretation is that in spite of the fact that the merger agreements indicate that Plan B is now part of Plan A, that that's not really so because the assets have not yet moved.  So I continue to file 5500's (and in my case get an audit) for Plan B until the assets are down to zero.

What do you guys think?

I agree with David but good merger amendments/resolutions will specify that the assets in the old plan are part of the surviving plan as of the merger date. 
 

I, too, agree with @david rigby and @Bill Presson.  It is worth noting that in a stock acquisition, the seller effectively "disappears" upon closing and is replaced by the buyer as the Plan Sponsor.  In effect the ownership of the assets happens on the merger date. 

In an asset acquisition where the seller continues to exist after closing - and particularly if the seller's plan continues to exist after closing with the seller as Plan Sponsor - then it is good practice to document who owns what and when do they own it, and settlement of plan assets will occur as soon as administratively practical.

@Paul I is correct.  However, it's worth noting that the original post said nothing about buyer or seller or multiple plan sponsors, only about a merger of one plan into another plan.  Careful consulting practices will help plan sponsors understand the difference as well as how to anticipate (and properly execute) such transactions.

Agree with everyone.  Upon the merger, the trust of Plan B effectively becomes a trust of Plan A along with the original trust of Plan A (or a subtrust of the trust of Plan A).

Also agree with all of the above if properly and sufficiently documented. As part of that - resolutions/amendments et al - I would also suggest that those should have been timely submitted to B's trustee/custodian and the titling on the account should have been changed on or about 12/1 as well.