Go Home, RSS. You're Drunk
When Adam used the term "standards" to refer to RSS feeds, what he was really talking about are RSS Specifications.
The current RSS Specification is RSS 2.0 (which is actually version 2.0.11 of the specification). This has been the standard since 2009.
Here's how I wrote to a client about this:
RSS specifications have changed over the years, with lots of incremental versions between when RSS first started being used and where it's at now. The current specification is 2.0.11, commonly referred to as RSS Specification 2.0.
Personally, I find it difficult to believe any site would be using an older specification, but it is likely that they might not be following the specification exactly, which can lead to issues parsing the feed.
For additional clarity, RSS is an XML document (a structured language not unlike HTML) that contains - typically - the last 10 pieces of content posted to a site (it can be configured to contain more, or less posts, as well as including the full or partial text of the post). As new content is added, the RSS file is updated to exclude the oldest content and include the newest.
Here's an excellent method of validating an RSS feed: https://validator.w3.org/feed/. If it throws an error there, we aren't going to be able to rely on it in RSS widgets or Feed Discussions.