For a grand total of 478 missions depicted so far in the Five Year Mission. And those don't count stories told through flashback in other adventures. There are quite a handful of them which I've not numbered. The vast majority of these tales take place in the final half of the five years, but for the sake of argument that rounds to about 94 adventures per year. It next occurred to me to see how many missions have been depicted by the crew of the Enterprise-D during her seven and a half years in service:
For a total of only 441 missions spread out over seven and a half years, for an average of only 59 adventures per year. I almost expected for there to be surprisingly more TNG adventures than Five Year Mission adventures, but it turns out that the obvious answer is that the Five Year Mission has been explored far more than even the TNG era.
What does this all mean? I'm not sure. But at least we now know.