ok now I understand your point of view.
In my opinion always there is a single SCCP connection for each mobile, except in the special case of an external handover.
And so you have a strict relation between SLR/DLR (sccp local references) and the mobile id.
But inside this SCCP cobbection you can establish more “application” (BSSAP) connections and they are identified by the field DLCI (=Data Link Connection Identifier).
These BSSAP connections have a relation with the radio links (LAPDm).
For instance you can have a connection for the current call and another one for the SMS exchange, because the LAPDm links are independent. Indeed they have different SAPIs (0 and 3).
In the A interface this is something redundant because the L3 message contains the protocol discrimnator, and so we dont need strictly the presence of DLCI to deliver the message correctly.
Anyway I agree with you that there can be a “distribution function” based on SAPI also.
More infos about this subject are present in 3GPP 48.006 par. 9.3.1