Sorry I’m not sure about GUIDs but I have an example
Article from the original feed:
<item>
<title>Some title</title>
<link>https://www.example.com/path/to/article</link>
<pubDate>Fri, 28 Feb 2020 10:20:00 +0000</pubDate>
<guid>https://www.example.com/path/to/article</guid>
<description>...</description>
</item>
Article from the news aggregator:
<item>
<title>Some title</title>
<link>https://www.example.com/path/to/article</link>
<pubDate>Mon, 02 Mar 2020 02:46:03 +0000</pubDate>
<comments>https://news.ycombinator.com/item?id=12345</comments>
<description>
<![CDATA[<a href="https://news.ycombinator.com/item?id=12345">Comments</a>]]>
</description>
</item>
I think in this item GUID is the link tag value, right?
Thank you