I think most of the graphing tools will take care of this problem as long as they are aware of Timeseries (DB). e.g. Grafana. So I’m sure these tools have either already solved or working on solving the underlying issue.
Adding tags is also a nice approach but you have to justify the cost of the resources (for running Influx) vs this feature/functionality. But your approach is correct and should work. Maybe introduce a single Tag which contain both Month and year. The Influxdb allow tag searches using regex so single field solution can also work.