Never do SQL Server patching? I am aware of Brent's post Why Nobody Ever Patches Their SQL Servers in this regard.....and with one of my friend, please assume one such scenario, where nearly 100 SQL Servers are never patched. Assume that no bugs or performance issues have ever been reported by any user. So, is there a cool way for my friend to identify across all the servers - where he is unaware - and few of the servers may already be hitting some bugs? In other words, how to pro-actively find the bugs across 100 SQL Servers?

One plan is to read release notes of those bugs where bug could be identified using a server trigger on occurrence basis (may be) .... capture that in local tables....SSIS those at a central location.

But, does this plan seem worth?

Special interest on those bugs where some impact on data by any chance. (FYI, DBCC CheckDB with purity runs error-less). Or some possible loss to business.

And finally assuming that, indeed, some bugs detected in some SQL Servers - so, how and why to treat them as "threat" when no issue reported by users ever from many years?
I assume you're talking about me, and I'm not sure what post you mean, but here is my thought:

Patch your SQL Servers regularly.

I'm such a huge fan of patches that I wanted to make it easier for people to find the most current updates for SQL Server, so I built SQLServerUpdates.com.

If you ever want justification for why you should be patching, just go back through the list of hotfixes in each cumulative update that you've skipped. You'll find bugs that deliver incorrect query results, and that's usually all management needs to hear in terms of why we need to patch. 

Here are just a few fixed SQL Server 2017 bugs for incorrect query results - not an old, dusty version of SQL Server, but the brand new one they just released:


All transactions reported as completed even though some fail while trying to commit in SQL Server 2017
Incorrect behavior when you use memory-optimized tables with "where exists" statement in SQL Server 2016 or 2017
Returns incorrect results when computed column is queried after installing hotfix that's described in KB 3213683 and enabling TF 176 in SQL Server 2016 or 2017
Queries against PolyBase external tables return duplicate rows in SQL Server 2016 and 2017
Incorrect MDX query results if a table cross join is run on a table hierarchy member in SSAS
A data mask on a floating points column is not applied in SQL Server 2017 and SQL Server 2016
Divide-by-zero error when a parallel query is forced to run in serial mode in SQL Server 2017


And all that was only the first cumulative update. Want your query results to be accurate? Get your patching on.