If Mickey signs up for a medicare advantage plan during the open enrollment period now thru Dec 7th, the insurance won't take effect until Jan 1, 2020. You can sign up for a medicare supplement plan at anytime during the year, but if you don't do it during I believe the first 6 months when you turn 65 you have to pass underwriting. There are a few exceptions to this general rule.

KJ, the fact you had to pay some small amounts for you partner was probably because you had a less expensive plan that had co-pays. Plan F was the best and most comprehensive plan, but you can no longer get it unless you were grandfathered in. The second best plan is Plan G which I suggest you get for your mother.
https://www.medicare.gov/index.php/s...digap-policies