"Concurrency Limit" allocates that number exclusively to that integration. It will always have those available and can't use more than that. Anything you set here will reduce the available 'unallocated' pool (which is shown as 'Max Concurrency Limit' ). in your example, A can only ever use 6, and B and C share the 19. From 'Concurrency Limit Per Integration:

When allocating part of your account's concurrency limit to one application, you reduce the available concurrency limit for other integrations, which do not have a specific limit.