Trying to not "update" certain fields

I am trying to consolidate many, many lists which have been imported over the last 2 years, into 1 Global mailling list which I then plan to use Segments on to acheive the same effect of 50+ lists, but far more efficiently.

I have extracted all my lists and added the following information to them :

Date originally uploaded to Campaign Monitor
Parent Source (the sort of 'group' that this list covers i.e 2013 Promo)
Source  (the exact list that this information came from)

I want this information to preserve it's oldest entry. So we may have a person who was originally added in Jan 2013, but then reappears in a list in August 2013. Whilst we want their contact info etc to update, we want to know when they FIRST heard about us. For this we need to keep the oldest entries for the 3 fields i have added.

The only way i have found to achieve this is to upload the lists in reverse order (so the most recent list first). This means we keep all the important 'analytic' information we need, but we do so at the cost of data accuracy.

This is becuase we now have a database wherby the contact information is based on the oldest versions we have on file, rather than the newest.

And obviously if i add any more names to the list, if they already exist then it'll over-write those important 3 fields again and i'll be no better off.

So after 2 days of working on this i now have an accurate 'snap-shot' of what our database looks like today, and where everyone came from, but that's it.

Is there any way i can tell Campaign Monitor to upload List x, but dont update specific fields if there is already info in them?

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