Below is a helpful and informative post I found online regarding case transfer from NBC to FO (and eventually FO to NBC...)
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You will never get a transfer notice from NBC to a field office because it's not a physical transfer unlike when a case moves from one service center to another. There are 6 service centers ( Texas, Nebraska, California, Vermont, Potomac and Missouri that is NBC) . Under NBC, there are 89 field offices. When case goes to FO from NBC, it's an electronic transfer unless it's going to local FO for interview. Any transfer between service centers is an actual physical transfer of case papers and hence you get notified and get a physical receipt. 'Case transfer' status means, service center which had your case till now confirming transfer. 'Case transferred and new office has adjudication' means new office had accepted the case adjudication. By the way, these statuses are just and electronic translations. Look at it as a bank transfer. First status is like you sent a check to a party through your bank, second status is their back acknowledging that they received the check. It take few days the party will receive the cash. Same here, after these two statuses show up, it takes 2 to 4 weeks your case is physically transfers and get routed in at NBC. Once it receives in NBC, it electronically gets transferred to a FO and that's when Emma agents will tell you what office it is. Until that happens, you will get random answers like, case is at NBC, case is still at TSC/NSC, case was never transferred or transferred back. Don't believe those answers. It will just raise your blood pressure. In my case, my case transfer status was happened on Feb 15th and 16th. Until 3/15 I was getting random answers. Finally on 3/19, agents started to tell me that my case was transferred to San Fernando Valley FO. So it took almost a month to transfer to NBC physically. Hope this helps..