Baseboard Heater and misc wiring ???

My understanding is that these are usually 220v with a 12/2 with ground on a 20amp circuit and the white wire is not used as a neutral, instead it is the 2nd HOT leg of the circuit.

I had my old 60amp panel replaced with a 200amp panel when I bought the house. It was one of the first things, I had done, so I don't really recall what circuits were in the old 60amp panel. It does seem there was a 20amp 220v breaker in the old panel, but I honestly can't recall. The new panel was done by a licensed electrician and inspected by the city and it passed code.

It is only recently, that I have been made aware of the wiring for the baseboard heaters, as I am looking into replacing the current one. Because of this I have been curious how mine was wired, so I opened up the panel and looked.

It has either 10 or 12 gauge wire, on a 110v 20amp circuit, but the white wire is going to the neutral/ground buss bar.

Is this likely correct or do I need to open up the baseboard and see what it says inside? Will it say?

The heater works and I used it all last winter, but am now concerned about it being wired correctly. I know it was inspected and wired by a licensed electrician, but it's not like the city inspector looked throughout the house to see what all was installed.

I do sort of question some of the workmanship of the electricians as the panel wasn't cut in very nicely and some other things seemed kind of hacked together to get stuff to work. I'm not upset, the room the panel is in is/was slated to be gutted of lathe/plaster/drywall and redone, but still makes one question.

The other questions are there is a 12/2 ROMEX® wire going to a junction box which housed a light on a different circuit. The 12/2 wire is tied into a BX cable which feeds what is currently my laundry and not sure what else is on circuit if anything. The 12/2 wire is on a 20amp breaker, how can I be sure the BX cable is 12gauge? Should I worry? This is something I do plan on actually eliminating in the near future as the laundry is moving to the basement and the old room will become a pantry with all new wiring, but in the meantime, I am concerned.

What is common practice when pigtailing wires in a junction box? Electric tape or not over the wire nut? I wonder, because I always use it, but the electricians didn't use it on any of the boxes, I opened. Is that safe? Or is it just preference?

Thanks for any replies and sorry for the bit of rambling and multiple questions...

Just went looking at a few other things on some of this wiring and another question comes to mind....

Why does some of this old ROMEX® wire look blacked on the outside? Has it been overheated? Should I get that wire off the circuits ASAP?? Or is that just something some of it does with age?

One spot is in the crawlspace under a kitchen boxout, the other is where some wire has been ran along a portion of wall space and been painted white at one point. The one that was painted white, looks almost like someone held a flame to the area quickly and moved it away. Kind of black in the center with golden brown around the edges. The wire itself, though discolored, looks and feels fine, it hasn't been apparently melted.

As I type this, I am thinking this will be my next tackle, as these are really the only "old" wiring circuits left in the house. All knob and tube has been torn out and replaced, these circuits are part BX, part silver/black ROMEX® and part ROMEX® from probably 80's to early 90's. I just need to know if I should shut those circuits off and leave them off or if they are likely ok for another week or two.

Thanks again.... I can get and post a pic if need be.