The opportunity code looks like a good candidate for a primary element, but it might not be the only one depending on what you are trying to protect. I guess for some roles opportunity codes are critical and always included in conversations about data in CRM, but other roles only care about tenant IDs, names, subscription IDs, etc., so it always depends on which permutations of data need to be detected. Also, while some scenarios are about detecting data that came from the data source (e.g. data extracted from CRM), in others the objective is to use the data in that source to pinpoint sensitive data even if it came from entirely different sources (or even manually entered into an email, e.g. during a support conversation with the customer), in which cases identifiers like opportunity ID or contract ID are less likely to be present.
In the follow up webinar we will go over a structured process to decide which columns to use as primary elements based on the column permutations of interest, so stay tuned!