Hi there, thanks for asking, and welcome to the community! Your interpretation is correct; for any voting round, prompt fills should not be posted anywhere else, including the community's AO3 collection, until the voting results have been posted. The reason is basically to keep the voting fair for everyone; a fic that's posted/previewed on AO3, fic communities, or in fandom newsletters will end up with a lot more votes than one that doesn't have that kind of reach.

This does not apply to Amnesty rounds, where there's no voting period, just a roundup at the end.

I hope that clears it up! Let me know if you have any more questions and I'll do my best to help!