Sometimes the metadata used to represent a change made in Salesforce doesn't quite line up with what the Salesforce UI would lead you to believe. An example of this is picklist values on Standard Fields; for instance, the values of the Account Source Field on the Account standard object.

The Salesforce UI makes it look as if the field actually stores the value, but the reality is that the values are stored in another metadata type called a Standard Value Set and the actual field definition for Account Source is only a reference to the Standard Value Set.

To find changes to your picklists, run a comparison that includes the Standard Value Set, Global Value Set and Custom Object metadata types in a custom filter. You can then filter the Gearset result and find the changes you're interested in.
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​Note: It is a documented limitation of the Metadata API that you are unable to delete a picklist value via the Metadata API. Instead the value becomes inactive.
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​Note: This behavior is the same for Custom Fields, as the Metadata API treats Standard and Custom fields as one type.