There is conflicting information around Salesforce IP addresses and whitelisting. Or maybe it is just confusing.
Exhibit A would be articles like this. They are official and comprehensive.
For example these comprehensive ranges for APNIC
The key word there is OUTBOUND, as in outbound from Salesforce. At least that is the context of the S4S connector, which uses a limited number of Salesforce callouts to retrieve analytics data out of Sitecore xDB or SQL.
These comprehensive whitelists are related to accessing Salesforce.com from corporate networks where web browsing may be restricted. In the case of authorising Salesforce callouts, you can pull the originating IP from IIS logs and whitelist that IP.
For example 188.8.131.52 has been a common APNIC callout for us. If you were to whitelist everything in the Knowledge Article at the above URL, you'd pick up this IP, but that would be going much further than you need to.
Occasionally there is a pod re-org and we see a new callout IP pop up, but it is rare.