We allow this, and have called them iterative reviews. Here's the original meta post that asked if they're okthe original meta post that asked if they're ok, and if you have any queries about the specifics then we have a tag on Meta for them: iterative-review.
replaced http://meta.codereview.stackexchange.com/ with https://codereview.meta.stackexchange.com/
replaced http://meta.codereview.stackexchange.com/ with https://codereview.meta.stackexchange.com/