Google Tag Manager - merge data from "old" analytics

Question

I have a site which uses the old Google Universal Analytics with a "Tracking-ID" (UA-XXXX).

Now i have created a container (and published it) inside google tag manager, inside "google analytics" i have "Upgraded to Google Analytics 4" via the button, this created a new entry in "properties".

This new property does not have a Tracking-ID but a Measurement-Id. Inside google tag manager in the newly created container i added a Tag "Google Analytics GA4" with the above Measurement-Id, and a trigger "all pages".

When i visit the site i can see inside the "real-time"-Overview my own "visit".

But on the Main-Chart (where i can see when how many users visited the website) the "old data" from Universal Analytics is still missing.

How can i "include" the old data into the new property?

Is that even possible?

Answer 1

No, that's not possible. Moving old data into a new property has never been possible, and in this case the data models are different, so it would probably do not make a lot of sense.

If you want to reconcile old and new data you could do it programmatically by using the API (or BigQuery exports if you have GA360 for your old properties) and doing some mapping in code, or you could probably use Data Studio and merge old and new data, if you finde a shared field that you can use as a key.