Typically the work in a paper, if substantial, is done over a long time, so even if the main destination ends up being same, it's unlikely the route and sidesto

Typically the work in a paper, if substantial, is done over a long time, so even if the main destination ends up being same, it's unlikely the route and sidestops are the same. So often you can wriggle a little bit and expand the paper sideways, so that it is still publishable work even if the other work is given priority. It's actually not that rare to have similar papers appear in arXiv one or two weeks later after you submit --- to me, it happened several times within last few years. In these cases, it is possible to see that the approach differs enough (and moreover, often you know the people in question, or you know someone who does).