Are any custom SQL queries able to be added as series?

The docs say you may not be able to add a custom SQL question as an additional series to a dashboard panel, but they seem to imply you can in some cases.

In what situation is it possible to use them as additional series, or is it just not possible?

Hi @lawrencejones
A link to the docs page would be helpful for context. You can use SQL as long as they have similar structure.

The two custom SQL queries are as close as could be, with the same dimensions and time component for the x-axis.

In terms of the docs, it's under: Dashboard for Charts with multiple series | Metabase

SQL questions may not work . Metabase has less information about SQL-based questions, so we cannot guarantee they can be added reliably. You’ll see a little warning sign next to SQL questions to indicate this uncertainty, so be aware that adding these kinds of questions may not work.

The 'may' is what I'm asking about, as it implies this might be possible but I'm unsure what specific circumstance needs to be true.

@lawrencejones If the SQL have same timeseries structure, then it should work.
If you cannot get it to work, then post the metadata for both questions by going to /api/card/123, where 123 is the question ID.