5.14.7 TransferSubscriptions
5.14.7.3 Service results
Added text for Bad_NothingToDo:
The result is used if the subscriptionIds array is empty or if the old and new session are identical.

The solution sounds a bit confusing, so I ask to be completely clear.
The entire service shall fail and do nothing if any of the selected subscriptions is already attached to the session?
I would have expected an operation result, but it is true that a good, bad or uncertain operation result would be confusing.
I assume the goal is to prevent a special handling for the single transfer operation, too much complexity for too few benefit.

A client which got out of kilter and forgot which subscriptions it already has may have problems to recover.
On the other hand side, there are ways to test which of the known subscriptionIds are owned by the session, like GetMonitoredItems.

Agreed to return BadNothingToDo in the operation level result instead of service level

Table 102 – TransferSubscriptions Operation Level Result Codes
Added
Bad_NothingToDo
See Table 182 for the description of this result code.
This result code is returned if the Subscription is already owned by the Session used to call TransferSubscription.

Agreed to changes edited in F2F.