One SEO professional asked John Mueller if there were any negative implications to having duplicate URLs in your XML sitemap files?
Their question was: Can you have duplicate URLs with different attributes in your XML sitemap files? For example, one URL in one sitemap has an hreflang annotation, and the same URL in another sitemap may not have that annotation.
John explained that from Google’s perspective, this is just fine. This happens every now and then that some people have hreflang annotations in sitemap files, specifically separated away, and then they have a normal sitemap file for everything as well. And there’s some overlap here.
From Google’s perspective, they process the sitemap files as they can, so they can take all of that information into account.
And there is no downside to having the same URL in multiple sitemap files. The main problem is if you have conflicting information in the files.
For example, let’s say with hreflang annotations, this one is for Germany. Then another sitemap file might say “this page is also for France, or in French.” Then Google may be saying “what is happening here, we don’t know what to do with this kind of mix of annotations.”
Therefore Google will end up picking one or the other. Similarly, if you say this page has been last changed around 20 years ago ( which doesn’t make much sense), and another sitemap file might say five minutes ago, then Google will say something like “well, one of you is wrong. We don’t know which one, but perhaps we’ll follow one or the other. Or maybe we’ll ignore that last modified date entirely.”
So that’s something that you have to watch out for.
Otherwise, make sure that the sitemap files are all consistent with each other, and that they work together, and they don’t have conflicting annotations.
This happens at approximately the 16:38 mark in the video.