Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% and the 'number' property is already documented in detail (formats, space/comma/slash handling, kind-code retry). The description only restates 'as printed on the document' and 'a trailing kind code is handled for you', adding little beyond the schema, so the baseline 3 applies.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.