You might be looking at the chart on your profile page? Like this?
If you click through a city from your profile page & open that right tab in that page, it should include the purple Percentage box & the right axis should be labeled “Percentage Progress”
I think you’re right that the charts will get more detailed as either your history syncs in (with the caveat around Garmin’s recent Fun™ change) or as you complete more activities.
Update: I just found you in the site & your data isn’t private, so I could poke around.
You just need to click the “Reset” button in the view you shared - it’s currently filtered to just this past few days, but the default looks like it goes back to 2021.
Your chart in Evanston is similarly filled out back to that date.