Hello,
If I understand correctly is your process to create duplicate contacts in order to allow assignments to your Business Sector field which might probably is of type option set. This does not sound like the best design.
You could look at different approaches to clean up your data and find a better design.
Option 1: Create a separate object for your Business Sector and build a 1:N relationship that can associate contacts under Business Sectors. On each contact you will then find a grid of Business Sector which the contact is attached to. This pattern is great if you need to maintain more information under your Business Sector entity.
You would also build dynamic marketing lists for each Business Sector that select the relevant contacts. You can distribute campaigns against such lists. You will also be able to build marketing segments, if you are using as well Dynamics 365 for Marketing to drive your marketing automation in that app.
Option 2: Use a multi select option field type defined within the contact or on global level for your Business Sectors. Now each contact can be associated to one or more sectors by setting the respective multi choice options.
Again you would also build dynamic marketing lists for each Business Sector that select the relevant contacts. You can distribute campaigns against such lists. You will also be able to build marketing segments, if you are using as well Dynamics 365 for Marketing to drive your marketing automation in that app.
Option 3: The lightest option would be to simply create static marketing lists, one for each Business Sector and add the respective contacts to those lists.
You can distribute campaigns against directly against those lists. You will also be able to build marketing segments that load contacts from those lists, if you are using as well Dynamics 365 for Marketing to drive your marketing automation in that app.
But the last option is the most fragile one, because modification of the lists are easily made and you would use your Business Sector association.
Best end to end approach would perhaps be:
Use Option 3, just as a starting point when you identify the contacts per Business Sector and deduplicate contacts. Then you can start from these lists do update all respectively contained contacts for Option 1 or Option 2.