"Selling plans are grouped together in Liquid when they are created by the same app, and have the same selling_plan_group.name and selling_plan_group.options values. For more information, refer to theselling_plan_groupobject."
One the front end, the groups
Also on that page:
Selling plans and associated records (selling plan groups, policies, and associations to products and variants) are deleted 48 hours after a merchant uninstalls their subscriptions app. Products and variants themselves are preserved. We recommend backing up records if you need to restore them later.
So on the product pages, we will group "identical" selling plans. Once a customer checks out, subscription contracts will be created and those will determine how the customer is charged (and contracts can be modified in certain ways). At that point, a selling plan/group could be deleted and it will not have an effect on existing contracts.
In summary, the duplicate groups may just cause confusion on your end, but for customers should not be something they really see or know about.