Buyer Contributed to Seller's Plan after Asset Sale

Company A acquired Company B in an asset sale in late 2018.  Company B maintained a 401(k) plan that was not assumed by Company A as part of the sale.  Nonetheless, following the closing date, Company A has continued to make contributions (both employer contributions and elective deferrals) to Company B's plan, which were accepted by the TPA.

It seems to me that this scenario results in countless technical violations, but little (if any) harm to participants, and that the least problematic solution would be for Company A to assume sponsorship of the plan, retroactive to the date of close.  I'm aware that such an approach should involve a VCP application, though I doubt the parties will be interested in the time and expense involved in such an application.

Any problems with that proposed solution (aside from the risk associated with not going through VCP) that I'm missing?  Alternatively, are there cleaner approaches that people have used or seen?

Was the contribution made in 2018 or 2019?

I think the plan might be able to return the contribution to company A.  I would argue it is a mistake a fact or maybe it is not deductible under 404 (though I admit I would want to research both in more depth).  You might also argue the contribution is not a plan asset because the plan never had a right to that money.  For example, if by mistake a bank erroneously sends $10 from my checking account to a qualified plan that is unrelated to me, and the trustee erroneously accept the $10, that doesn't make the $10 a plan asset.  Similarly, if a mutual fund credits earnings to the wrong plan, those earnings are not a plan asset of the wrong plan.  Its the same thing here.  Company A made a mistake and sent a contribution to the plan that doesn't belong to the plan.  The plan has no right to the money.  I know a bank or a mutual fund is not an employer for purposes of 403, and arguably Company A is here.  I just think this is different than returning money to a sponsoring employer.  But again, I would want to look at that more closely.  

My thought would be to try to find sufficient documentation to have Company A as a Sponsor/Participating Employer for Company B's plan.  (That seems to clearly be the intent, perhaps there is enough documentation to satisfy the burden.)  Alternatively, Company B could assume Sponsorship of the plan today.

Under either approach go to VCP to get a blessing.