As an accountant, I highly recommend FA-Development Team to switch to 2-Fiscal years mode
as this is vital and necessary for multii-users, multi-localtion, multi-period entres.
Especailly during the year-end cut-off time.
If we just control it to one year, other users might not aware this and will complain for errors which are unnecessary.
For safety, you can give the superadmin the right to temporarily shut down some period so that no one could change it without the permission of superadmin.
Many contemporary propietary accounting softwares already grant at least 2 years for theirs customers now, like MYOB, peachtree.