since the funds are outgoing, i'll assume the recipient of the intended wire is the blocked party. likely you won't have their tax ID number, but if you've debited your clients account to transfer out, an argument could be made that the funds are no longer your clients.
of course, since it is ofac held and you are opening a "new" account to hold the funds until OFAC gives permission to release, your questions are more for internal purposes based on what your system requires when opening an account, rather than regulatory. OFAC won't care how it is titled as long as you can show the funds were held and you can provide that audit trail.
we used to open a new account and hold, but now we simply place in an internal GL, although it has been years since we did. and yes, paying interest and sending a 1099-INT to the client that was sending the funds is a requirement.
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