Enrollment Material Deadlines & MDOs - What are the regs?

[OrderOfOps]

Hi all,

A participant satisfies the eligibility requirements of 21 and 3 months in August 2025. Because of a mix-up at the Plan Sponsor HR's department, they were not provided enrollment materials (SPD & Annual Notice) at that time. This seems to constitute an MDO, with necessary corrections outlined in EPCRS.

What if the participant received the enrollment materials well advance of their entry date, say on their date of hire in May. My recollection is that this is permissible, but I know certain other items have a 'reasonable period' defined with 'no fewer than 30 no more than 90 days prior' language. If this is permissible, would this no longer constitute an MDO since the participant received enrollment materials and could have made a deferral election on the Plan's website at any time?

Hoping someone can direct me to the governing regs themselves. Appreciate y'all!