The ADL User Guide for Open-AT v3.03 says, on p42,
But this doesn’t seem to be always true! 
If the remote party hangs up the call very quickly - after the adl_callAnswer, but before the ANSWER_OK event - the flow may not be automatically unsubscribed; eg,
182.991 Trace L3RR 1 Unable to find the string of the remote trace in the file (ID = 4795)
199.075 Trace L3RR 1 Unable to find the string of the remote trace in the file (ID = 4795)
200.537 Trace IP 21 Get Mem 01CC0832
200.548 Trace IP 20 [ADL] tmr subs ; id 3 ; hdlr 100114CE ; val 30 ; cycl 0
200.557 Trace IP 10 vlk_callSvcHandler Ev=1 Id=0
200.567 Trace IP 10 ADL_CALL_EVENT_RING_DATA
200.577 Trace IP 10 vlk_callFsm Ev=0 St=0
200.628 Trace IP 27 Call subs 10011604 : 0
200.637 Trace IP 25 FCM subs 0 : 1
200.647 Trace IP 10 adl_fcmSubscribe = 1
200.658 Trace IP 10 vlk_callFsm NewSt=1
200.688 Trace IP 10 vlk_fcmCtrlHandler Ev=0
200.697 Trace IP 10 ADL_FCM_EVENT_FLOW_OPENNED
200.707 Trace IP 10 vlk_callFsm Ev=1 St=1
200.728 Trace IP 10 adl_callAnswer = 0
200.738 Trace IP 10 vlk_callFsm NewSt=1
201.037 Trace MMT 1 Unable to find the string of the remote trace in the file (ID = 24284)
201.037 Trace MMT 1 Unable to find the string of the remote trace in the file (ID = 24285)
201.048 Trace IP 21 Get Mem 01CC097E
201.068 Trace IP 10 vlk_callSvcHandler Ev=3 Id=1
201.078 Trace IP 10 ADL_CALL_EVENT_RELEASE_ID
201.098 Trace IP 21 Get Mem 01CC0A72
201.118 Trace IP 10 vlk_callSvcHandler Ev=9 Id=0
201.129 Trace IP 10 ADL_CALL_EVENT_ANSWER_OK
201.138 Trace IP 10 vlk_callFsm Ev=2 St=1
201.148 Trace IP 10 vlk_callFsm NewSt=2Note that the ANSWER_OK event arrived after the RELEASE_ID event, and there is no FLOW_CLOSED event
Is there a complete description of precisely what all the call Events mean, and exactly when they can happen?
The list on pp69-70 is pretty vague! 