1. COBOL is a generic term that's used to describe the programming language, the compilers, runtime libraries, the object code, etc., so this could be a variety of things. However, since your question seems oriented to compilers, I'm guessing you mean the original COBOL compilers from IBM, which were replaced by VS COBOL II.
The specific name for these compilers was the OS/VS COBOL Compiler and Library (5740-CB1). OS/VS COBOL is no longer supported by IBM (although equivalent runtime support can be accomplished through the use of Language Environment), and it only supported 16-bit addressing. It was quite cumbersome when it came to addressability, using a facility called BLL cells, and had other limitations.
2. VS COBOL II (5668-958) replaced OS/VS COBOL in the early to mid-eighties, and it provided 31-bit addressing as well as changing the language structure to make addressability easier through the use of pointers and other facilities. The migration was not transparent in most cases, though, and often some degree of application code modifications were required to upgrade to VS COBOL II.
VS COBOL II was replaced with COBOL for MVS & VM (5688-197), then COBOL for OS/390 & VM (5648-A25) and the current version of COBOL is called Enterprise COBOL for z/OS & OS/390 (5655-G53). Like OS/VS COBOL, VS COBOL II is no longer supported by IBM, and equivalent runtime capability is provided in Language Environment.
3. MFCOBOL is a generic term for the COBOL provided by MicroFocus through the use of compilers built into such products as Micro Focus Mainframe Express, Micro Focus Object COBOL Developer Suite, and Micro Focus Revolve. These products are much more than just compilers and libraries; they include a variety of development tools in addition, all packaged together. You cannot order MFCOBOL by itself.
In the case of the mainframe, these Micro Focus compilers provide equivalency with the IBM compilers mentioned above, but MFCOBOL is also used on other platforms such as UNIX, and MFCOBOL is also packaged into other vendors' products, such as Sun and Hewlitt Packard. IBM also has COBOL for other platforms, but they are separate products from the compilers mentioned above.