Hello, 

In Odoo V15, subscription was an object sale.subscription. Migrating to Odoo V16, sale.subcription has been converted to sale.order
So there is no difference between an order and a subscription. It's now a parameter of the same object. (Recurrent or not)

The biggest problem we encounter now is :

   - Orders that are open (not already signed) in V15 with recurrent Article.

   - We migrate to Odoo 16. 

   - Orders are signed after migration.

Problem : No subscription is listed after signature because the order is not "recurrent"

How did you manager the problem with the migration ?