@roofy love to know where you're getting your information from on shiftys product architecture. If you have any more information on this, id love you to share this with the forum.
As the products were built in isolation, of course they are built on a different code base.
imo, and from what I've seen on their API docs, the product suite pulls from the same DB, where data is parsed via a middleware between the shifty subsidiaries.
by your logic, if a company is a customer of biz Dev, shifty and scheduler, then the customer is the source of truth and the customer requires 3 different integrations to support the product suite.