Migration to CJA from AA - Merging Historical and Future Data in CJA

I have a situation where we are migrating a number of digital properties (web and mobile apps) off of Adobe Analytics and onto Adobe CJA.  We would like to retain AA historical data within CJA, and so we are thinking to use the Source Data Connector to pull data from AA to AEP/CJA.  After that, future data would be collected via WebSDK and transmitted to AEP via XDM. 

From a CJA perspective, the ideal state would be the ability to create Analysis Workspace projects and panels containing data from both historical and ongoing collected data (via WebSDK > AEP) in one table or visualization, irrespective of how it came into CJA. 

A simple example of this might be a listing of site visits broken down by month; for this example, let's assume that 10/1/23 was a cutover date from AA to AEP/CJA.  A user would be able to create a simple report in Workspace by selecting the Visits/Session metric (or whatever we've named it in the CJA Data View) and the Month dimension, and the report would render the data as one would hope (and no one would be the wiser that anything interesting occurred on 10/1/23).  This particular example probably works just fine, but how about custom events/dimensions?   

Suppose you had an existing AA event and eVar - event1 and eVar1 - that you will be representing in CJA as some named metric and dimension.  Similar to the example above, you'd like to be able to build a single workspace panel in CJA that relates these two pieces of data and be able to have the time range span the cutover date from AA to AEP/CJA.

Does something like this rely on utilizing the same schema for historical data vs. future-collected data?  Initially, I was thinking to use the default schema when using the Source Data Connector to pull data into AEP from AA since that is quick to setup and get working.  However, our intended XDM schema in a WebSDK->AEP->CJA world would look very different, of course. 

Would derived fields be another approach for this?  Any other options I am overlooking?

Thanks in advance for any ideas or suggestions!