Leaving aside the IRS for a moment ... another consideration might be what the Ninth Circuit recently opined about SPD provisions:
"Assuming that Platt only received the 2022 email containing the new SPD, this email did not provide sufficient notice of the arbitration provision because the provision was buried on page 153 of the 170-page SPD. It is unreasonable to expect that Platt would notice a new arbitration provision hidden in a lengthy document."
[Platt v. Sodexo, S.A., No. 23-55737 (9th Cir. Aug. 4, 2025)]