Sorry, I'm a layman ;-)
Since 2012 I use the Edge 500 and a lot of activity data on my Mac. Because the Training Center Software does not support newer macOS versions, I have started with Garmin Connect and have imported all my old activities. This worked fine, and I can display all my old activities.
But it seems that for some analysis activities the Connect system does only use those activities, which I have imported new from my Edge 500. I'll try to explain that with an example: After I had imported some 500 activities since 2012, the information "Show personal records" (i.e. best performances) remained empty. Only after I had imported my todays activity, exactly this activity becomes suggested by "Show personal records"
I hope that this behaviour is no "feature", but that I made something wrong, which I can correct now.
Many thanks for any help!
BR Falk Kuebler