Unfortunately, you cannot make only some text inside a text frame partially transparent. But you can achieve the effect you’re looking for with various workarounds. For example, you could select the text you want to be semi-transparent and convert it to outlines (type > create outlines). That will convert it and anchor it in place; now it’s an anchored object, and you can set that to be transparent.

You could also create this effect with two different text frames, one on top of the other, where one frame is transparent and the other isn’t.

And, okay, I need to add this other article here, not because it’s relevant to you, Paul, but because it’s such a cool tip and I had no memory of us publishing it! Fascinating idea:

Using Paper Color to Help Distinguish Various Files

So glad you got that worked out! It is scary when stuff like that happens and it’s unclear whether it’s the software or user error.

But to answer one of your questions, there is a way to tell what version the document was created in:

Tip of the Week: Accessing Document History