CC ( Commercial Controls) was a replacement bolt for rebuild purpose. It is not original to a Smith-Corona. I think you are correct in assuming a Smith-Corona bolt would be marked with an "X" on top of the bolt handle are maybe not marked at all. Some examples, I've read about, had a single digit stamped on the root of the bolt below the handle.

Other posters may have other information. I"m a newbie but learning.

john