Hey everyone - sorry its taken a while to respond.
So yes, I agree there are probably multiple ways to make this happen - we even had a slightly different method in our old Dundas Dashboard solution. However, when we migrated to Dundas BI, I was able to make this even slightly more simple - and without using anything API related.
At a high level, it’s utilizing the Dundas annotation ability for a dummy data point. We have a stored procedure data cube that takes in the selected Year and Salesperson ID via bridge parameters and returns the same two pieces of data along with a dummy data point (same for everyone) of simply the integer 1. Then on the dashboard itself, we use this data cube via a data label control where the data point of “1” is the same color as the background (white) and therefore, hidden. Then Dundas basically takes care of the rest… you can annotate on this data point… and it gets tied to the selected sales person and year because of what gets returned from the stored procedure. An obvious downfall of this method is that when the year changes and the selected default year changes with it, unless the user changes it to the prior year - the previous year’s notes will not show. With a little training - our users are accustomed to this now! Hope this helps!