How can we distinguish the already enrolled and and the new enrollment for a plan in fast formula

Summary: I am trying to create a post election edit fast formula where I need to validate the options selected from two plans and checking the correct combination of options from the plans , if combination is not correct, fast formula should throw error at the time of submission of new enrollment.

Content (please ensure you mask any confidential information): Currently Fast formula is looking for the already enrolled in the respective plans, if in previous enrollment, options are selected wrong then fast formula is throwing error at the time of evaluate life event and it's not allowing to correct the option.