TIFF has been around for a long time... I've been dealing with it since the 80s. It is a very flexible format, and there have been a lot of different approaches to tagging them, from many different vendors. There are supposed to be standards, and even private tags are supposed to be registered, but the reality is that over the decades that has not always been the case. Many vendors have behaved rather loosely towards the standards.
It is very easy to find a program that will only partially understand TIFF tags from another program. Because TIFF can hold almost any type of image data, it is used as an archival format by a lot of different institutions. But over the years I've found it is also the format most likely to have metadata compatibility issues.
I don't know if this is what's happening in your case, but it could very well be, and you probably wouldn't have too much difficulty in finding another program that doesn't read all the tags correctly.
It's hard to assign blame when there is so much to go around.
There's a program called PhotoMe that you could download. They do a pretty good job of providing broad tag support to a host of formats. You would be able to re-save or re-tag in that, and it might fix the tags enough for MC to understand them.