How can I tell what is changing in Salesforce as they patch each pod?

There is a "current patch" view on the Known Issues site. Arguably this is the most important single piece of information, i.e. the stuff that is about to be fixed.

And you have inferred the correct structure of the query param. You can even see this if you use the following:

https://success.salesforce.com/issues_releases_view?release=198010000

You will see the current release. But the following indicates release in progress (as of the time of this post).

https://success.salesforce.com/issues_releases_view?release=198011000

Clearly the release team is trying to communicate the information you want, it just isn't very clear how to get to that information in some instances, and how it works (what is the numeric code that corresponds to a release, what are the patch numbers, when were they released, why is history incomplete, etc.)

I would suggest that this should be an idea on IdeaExchange, to the effect of, "Greater transparency and clarity in patch releases with regards to affected features, services, instances, and history."

I know that "have you tried IdeaExchange?" can start to be a pat answer from a Salesforce employee (like me), but I truly believe that this is precisely the kind of feedback that the technology teams should be getting from customers and implementers. You can also use it to suggest the level of documentation needed.

In fact, there is already an idea that is asking just that, 2 years old, with a measely 3 votes. If everyone who up voted for this question had voted instead, it would have increased the point count by times.

Some specific comments to clarify how what has been done already could be improved might also be good.

(Strike that...4 votes, as I just voted.)

Please vote for Easy navigation/searching for Scheduled/Fixed issues by release.

Update: Current idea point count as of Dec 2017 is at 390. If you up-voted the question above (or for this answer), then please vote for the idea!