The field list that can be found under Customization > Workflow > Workflows > Edit the Workflow > State > Set Field Value action > Parameters > Field contains fields from all Sub Types; not just from selected ones.
- Record Type is Transaction
- Therefore the Field list (screenshot below) will contain all Sub Types of Transaction (Sales Order, Purchase Order, Transfer Order, Opportunity, etc.)
Set Field Value action
- Location field can be found on the Sales Order record
- Opportunity/Estimate Status field is NOT on the Sales Order record
- This proves that the list depends on Record Type, not Sub Type
- There is a request for enhancement aiming to this.
- If fields are not showing on record, check Customization > List, Records & Fields > Forms as well. Some of them may be set to hidden or labeled differently.
- For list of relevant subtype fields please check Record Browser