Here's how I read your words:
"The gift of prophecy in the NT refers mainly to expounding on the written word of God (whatever was then available, which was primarily the OT).
I am unaware of a single case of that. Every case I can think of is God speaking something new and specific, such as Agabus prophesying that Judea would undergo a famine, and later that Paul would be bound hand and foot.
I don't see anywhere that someone expounded on something from the OT (or even early NT writings) and such was called "prophesying".
OK. First off, there are no more prophets that are equal to the prophets called of God in the OT. EACH Christian now has the Holy Spirit indwelling them; a major change from how God dealt with His people before that event. I refer to the NT gift of prophecy not in a manner suggesting that they were using the OT although I guess I might understand how you could see it that way, but I am not referring to the OT when I wrote what you are referring to.
Prophecy is referred to more than the other spiritual gifts and Paul says this, So, dear brothers and sisters, be eager to prophesy, and don’t forbid speaking in tongues in I Corinthians 14. As you mentioned, there were prophets active in the NT that we can read about, both men and women.
Something that does not seem to be done regularly these days, is judging the prophecies of the 'prophets' which the congregation to which that person(s) prophesy are supposed to do. Further, we are instructed that the prophets should speak two or three and that their spirits are subject to each other. Much like tongues, prophets have gone off the rails and can be found spouting any number of so called revelations that are supposedly from God but cannot be found in scripture anywhere....not referring to an event here but that this or that 'revelation' is from God when it can even contradict the Bible.
Can a prophet foretell the future today? I could call myself a prophet if that is all there is to it but I certainly do not think that would apply even though I have foretold some things that did happen and sometimes gave appropriate warnings to people or saw beyond a person's motives to what was really going on with them. If the prophets should prophesy by 2 or 3, that would indicate there is no prophetic leader in a church but we have those who think they are a prophet trying to take over a church in some cases. It's a mess
In I Corinthians 14, Paul states that 'you' can all prophesy so that everyone in a church might benefit. That would not be so if all people were doing was saying what was going to happen....predictive....rather than reveal deeper understanding of what is written...expound on the word. As it is, any prophecy should be appropriate to those to whom it is said and not something like 'God told me Harry was going to marry June or some such. I know of at least one disastrous such union, the result of God told me to tell you, that ended in divorce but not before the man in the case turned out to be sexually perverse and the woman was used and abused all because a 'prophet' told her what to do. Extreme you say? You might be surprised. I know the details because she came to me for help and wanted to be sure she was not being disobedient to God by leaving this bohunk.
I am sure also know that if tongues are interpreted they are considered equal to prophecy.
There is plenty more that can be said, but NT prophets are not to be confused with OT prophets even though people tend to believe that is their office if they think they are a prophet.