The check needs to go to each patch on the (patchwork) series and compare with the corresponding one on the git repository. If payload differ (or checksums), user should be notified and a v2 series must be sent. This task was originally discussed on https://bugzilla.yoctoproject.org/show_bug.cgi?id=8648#c5
We'll probably need to have a discussion with the community about how to handle this issue before we go ahead. Right now we don't officially place any restrictions on people updating the branch and it's relatively common practice, so we should establish whether we want to change that before we add this check.
As a first approach, lets see how often this practice is done by the community (sending a pull-requests and a bit later the branch is modified and no v2 is sent). Once we have this info, we can talk to the community about it.
At 2.4, the focus is on the python 2 to python 3 migration, tinfoil usage and stabilization of these two. So moving it to 2.5
patchtest in production executes in an isolated space (no network), thus there is no way we can do this check.