In the Query Tool (in web client or workbench), when we run a query that among other criteria includes Age (e.g. 55 year old), we expect that the patient set returned includes only patients of that age (e.g. 55).

It appears that the query filter simply looks at the individual’s birth date and does not attempt to actually determine their age. The age of a deceased patient is calculated based exclusively on their birth date, rather than the age of the patient at the time of their death.
In the "Previous Queries" view, the patient set returned by the query will display the age of the patient, which for deceased can differ from the age criteria of the query.