On bib records that have a mix of items with volume data and those without, it should be possible to place a volume-level hold that can be filled by the items with no designated volume. The wording can vary, but I imagine this would look like an additional option in the volume selection list during hold placement that says something like "No designated volume".

Currently, volume-level holds only really work if ALL of the attached items have volume data. In a large consortium setting, we try to keep our libraries consistent about this and run many reports to identify mixed records, but it's a constant battle that we cannot keep up with. If a single library adds volume data to a record that they shouldn't, then any holds placed before it is fixed are limited to that one item, and then after it is fixed would become unfillable holds. Allowing patrons/staff to place a volume-level hold on "No designated volume" in this situation would avoid this problem.

This fix would also make it so libraries that aren't splitting an item into multiple volumes don't need to worry as much about putting a "Complete Set" volume in just in case a single library does decide to split the items.