Updating memberships that have renewed in another system

Hello everyone!

Our museum is in a unique position with our implementation of Altru and I'm wondering if any of you may have had a similar situation or any thoughts on how we can move forward with updating our memberships. We began implementation nearly a year ago but had to pause and continue working with our previous system. At that time, we uploaded all of our constituents and memberships as they were at that point. Since then, we have not used Altru for renewals - we've used our previous system and have only used Altru for very specific things - online events & eTicketing, donations, etc.

Now that we are working on fully implementing Altru, I am wondering about the best way to go about updating our memberships. I've spent a lot of time learning about batch upload renewals but since member renewals have taken place in another system, I wouldn't be able to enter any payment info during the batch process. I also know that many of these members have taken actions that have been tracked in Altru since their memberships were uploaded last year - buying tickets for events, donations, etc. I've considered a complete re-upload of all membership data so that all of them would be current, but my fear is that we may lose the data we've generated from purchases these members may have made in Altru. I also know it may come down to a manual update for each member, but I figured I'd ask to see what you all think would be the best method before we consider how to do that.

Any suggestions would be greatly appreciated! I've spent a lot of time reading on this forum and so thank you all for your insightful posts and thanks in advance for any advice you can offer!