For a short period of time following an account switch, it will be associated to both consolidated accounts.

During our nightly reporting process, we parse consolidated billing files for new accounts and their linkages.  When linked accounts are moved between consolidated accounts, this results in the linked account ID being present in both consolidated accounts' billing file records.  When the account ID is present in multiple billing file records, we will show the linkage to whichever billing file was processed last.  This behavior only affects the Accounts page and will persist until the beginning of the following month, which at that point the linked account ID will only be present in one monthly billing file.  The accurate account linkage will persist after this occurs.

To verify that your linked account costs are now coming from the new consolidated account, you could run a Cost History report that is set to a Daily interval, filtered for the linked account that was moved, and categorized by Billing Accounts.  This report should show the costs transitioning from one billing account to another on the date the account was moved.