When does my employer coverage actually end? after 17 years as a payroll clerk

I was told my coverage ends on my last day, but the letter says the end of the month. I am in Denver, in case local advice matters. I have an appointment next week. Did coverage match what HR said?

Keep a copy of any coverage confirmation in case of later disputes.

Ask HR to confirm the exact date in writing. I also called the insurance company to double-check.