Sounds like two sets of books, to me. If I learn of other CU’s issuing similar notifications, I’ll be less concerned about it.
Any financial institution necessarily has multiple “sets of books”. The various assets and liabilities they have must be classified differently for reporting to different audiences. Regulators insist on a certain set of classifications, accounting firms which will audit financial statements require a different set, the IRS requires another different set, and customers require yet another different set.
If this change is pursuant to a recent regulatory change or regulatory advisory, then you may see other CUs issuing similar notifications. But it may well just be that they’re cleaning up an internal inefficiency that they’ve recently become aware of, in which case you probably won’t see other CUs issuing similar notifications.