Hi everyone,
I am currently working with CRM version 7 onPremise (about to update to 9.X somewhere in the first quarter of 2020 - hopefully...) 
If we delete a contact in the ERP-System, the Contact in CRM is marked as inactive. (unidirectional connection ERP -> CRM)
The Scenario:
The contact Anna has worked for our Customer KA000 for over 15 years, and we were able to gather a lot of data about her (example: Hobby, does she like our events, past e-mails, how should we handle her).
Now Anna decides to change her Employer and now works for LA999.
What the System currently does is to set the Record Anna of our Customer KA000 to inactive as she leaves the company and it creates a new Record Anna with a new ID for Customer LA999 as she starts working there.
As a Result we have "lost" all previously gathered data and have to start new. 
LA999 is being handled by another colleague than KA000 so there is no way that he knows about her history and might damage the customer relationship by handling her the wrong way... 
(lets say she hates to be contacted by phone or does not like our Events)
Since the entity contact has > 100.000 records  there is no way to do this completely manually. 
Anyone here with a similar Challenge? 
I was thinking about changing the Owner of the original Records to show them within the new Record.
The Problem with changing the Owner is, that it could get messy since the Sales department has to differentiate the old data from the new data. 
A Lookup Field titled "old Record" pointing at the old contact Record would do the same without messing with the new Data (or a new connection Role). Our Sales Guys could then transfer the relevant info into the new Customer ow review old conversations or notes.
To change a Owner via workflow or to create a Lookup-Field (maybe with autofil workflow) is easy but I need some sort of delta determination.... and a List of results which should be send to our Sales guys to do a last check. 
So the final check needs to be manual since we can not gather enough data to guarantee that a new found contact Anna is actually the same as the previously created Record Anna who has worked for KA000
I am the current System administrator / Customizer but self taught without proper Training. 
So I am able to customize the Systems components with standard customising, and I am able to write simple javaskript but I was not able to think of a construct within the CRM to achieve what I want.
I was not able to find a solution within the Microsoft Blogs but I just can not imagine that we are the only company with this Problem.