Adding a Subscription vs. "Move to Subscription"?

I’m hoping to provide multiple types of subscriptions on my site, based on different access levels.

The one subscription is finite (“Subscription A”:wink: and gives access to posts protected by shortcode # 1.

The other subscription is indefinite (“Subscription B”:wink: and gives access to posts protected by shortcode # 2.

I would like users to be able to subscribe to either or both Subscription A and B. But it seems that in Membership this is not possible. Users that are part of Subscription A have Subscription B presented on their account page as a “move to” option. This seems to mean that when they “move to” Subscription B, they loose Subscription A. But I don’t want them to loose anything, I just want them to be able to ADD a subscription to their existing subscription.

I realize that from the way my question is phrased it might seem the answer is to add a Subscription C that is a combination of A and B. But I cannot see how, for A is finite, whereas B is indefinite.

And in case it matters in devising a solution: “Subscription A” gives access to posts in the blog index that are set to expire after a certain period (currently this expiration is set with another plugin). The idea for “Subscription B” is to give access to different posts that are not set to expire.