Assuming the plan document and applicable law permits the interim valuation, I would provide everyone with statements to let them know that their accounts had been revalued based on a special interim valuation. I would explain to them why that was permitted under the plan document, etc. There are lots of reasons for this, e.g. employees and former employees may talk to each other and you don't want them to imagine things that the two groups were treated differently. Also, the separateds above the cashout limit might not want to take distributions if they see the new values are, so you want to send everyone their statements before you process their distribution elections. Also, the continuing employees may think twice about quitting once they see their reduced balances. Always dial in the law of unintended consequences.