Even though the Torah records these in separate places, and it appears to be written as two conversations, it is possible that both concerns came up at the same time, but for some reason, the Torah wanted to record these as separate events to teach us something else. Were there 2 separate requests?
I could not locate any commentary that says something about this either way. I surmise that B'not Tzlafhad would have thought about all the conditions of inheriting the land in their 1st conversation with Moshe, as they seemed to be "smart" girls.
If, in fact, these were separate conversations, was there some event that occurred that made them realize that there was a supplemental problem?