I see the word sentences repeated multiple times, but a lot of (good) content I see on Common Voice does not qualify as full sentences. For instance, the first green example in the OP, “The giant dinosaurs of the Triassic”, is a noun phrase rather than a sentence, as it lacks a verb. I assume then, given the examples, that both noun phrases and sentences are OK to add. How about other constructs, like adjective phrases and verb phrases?
This isn’t just to be pedantic about linguistics – I think it’s important to be clear in the guidelines, and I was genuinely confused by this when trying to pick sentences to add via the sentence collector.