There's a big penalty for delaying purchasing a Part D policy UNLESS your employer's insurance is 'creditable'. There are potential penalties for delaying Part A and B, but again, employer-provided insurance may prevent the penalties being assessed for/on you.
Medicare can't answer your questions, because they don't keep track of all the variations available. Besides, Medicare support is outsourced to a company that has received lots of complaints, so you can't rely on them unless you have to.
HR is your source for info. Sorry you have to wait until Tuesday, when they'll be swamped....