Would like complete-instances able to store value pairs: date, data

[BrucePlumb]

In my vault I have implemented a second list property parallel to complete-instances to keep hours spent on the task on each date. I have made a complicated formula in bases to map each date to the corresponding data so that daily notes can show that date's hours.
But it is a bit unsafe: The two lists have to be exactly the same length. If I accidentally click and delete an entry in either list it makes the dates relate to the wrong hours. If they were stored as pairs it would be much more stable.
Also I would like entering the hours (or whatever data) to work together with TaskNotes' convenient method of entering completion dates in a calendar.
I know that the properties widget doesn't handle property pairs but I can live with that. They look fine in source mode.