In overfunded DB Plan for Public 'Ees, could COLA for retirees' medica

[Guest songlaw]

In overfunded DB plan for Public Employees, where surplus would be used (partially) to fund COLA increase for retirees' health insurance coverage, could COLA be made retroactive? If so, what hoops to jump through? (For ex: Any maximum number of prior years for which COLA could be given?)