SharePoint Online List - External Content Lookup and data retention

Hello everyone.   I have an External content question I need help with, please? 

I've created a list in SharePoint Online for Open job inspections.     For each job there are a number of questions, along with the basic job info, city, st, address, etc..   I've created a database in Azure to store the basic job info.   What I would like to do, is use External Content lookup to retrieve the job info.  I've got this part working...    but my dilemma is this.    Eventually these jobs will close, and once closed they will no longer be listed in the Azure database.   I assume that once this happens, I will no longer be able to see the external content.   Is this true?   (We have sold over 100,000 homes, thus the reason for only listing "open" jobs in the db.)

Based on the above assumption, my thought was I would created a calculated field, and grab/write the basic information to my new list, so it is stored indefinitely.   The database has approximately 10 fields of information.   However, when it comes to creating a calculated field over the external db content, I only have access to the 1st and last fields.  Thus missing the 8 fields in between.   Is this a bug, or have I done something wrong with my setup?

Any advice would be greatly appreciated.   This is all new to me, so I'm not sure how best to proceed.

Thanks in advance!