If you're doing a batch campaign and two leads qualify that the system will only send 1. If it was a trigger campaign it would be a different story. You'll also just have to watch out for subsequent campaigns and making sure the 2nd record doesn't somehow qualify. Or the worst with duplicates is if one of your leads qualifies for a campaign say in your case where their license is active and another lead has a lapsed account so you send the latter record an email saying "Reactivate your Account!" and the contact responds to you in a confused manner asking why they're receiving this email when they're an active customer.
Is it 100% that you need to store those license tracks in a 1:1 single text field? Can't associate it as a related list one to many relationship?
Unfortunatelly, this is how customers are stored in our custom CRM and as they are updated in Marketo through API, even if i dedupe those leads and merge their license tracks in Marketo, they will appear again after the next update from our CRM
so i guess, i'd have to be carefull not to set up any trigger campaigns on the data values which may result in multiple emails