When symbolising on a single field that has a domain, the symbology list of classes picks up all the possible values from that domain, even if they are not all present in the data.
When symbolising on multiple fields (3 being the maximum), the list of classes is limited only to the combinations it finds in the existing data, rather than all possible classes, as with the single field option.
The GUI allows you to 'Add unlisted values' and manually add in the other possible combinations, however this is very time consuming.
It would be great to have an option to 'Add all unlisted values'. This would involve the software looping through the domains of the specified fields and forming all the different combinations it finds.
This would be really helpful, as when using 2-3 fields to symbolise on, it is common to not have every single combination represented in the data, but for future edits to use those unlisted combinations.
Note this could be more complex when using subtypes and subtype group layers, as it should look only for the domains that are relevant to that specific subtype.
