In both the case we can use "SY_SUBRC". It is system 
defined object. "SY_SUBRC" is mainly used in BDC Call 
Transaction and BDC Session. The "SY_SUBRC" object is used 
whether the records are Successfully Inserted or not, for 
that we can use "SY_SUBRC".

IF SY_SUBRC=0 -->Successfully Insert/Updated the records in 
table.
IF SY_SUBRC=4 --->Not Inseterd.Updated the records in table.

In call transaction return the "SY_SUBRC",because records 
are dump at a time. but where as Session not return.why, 
because if any error occurs in the program it will not open 
the first. i.e (BDC_OPEN_GROUP) so that it can't be read 
the data from the table.

The main thing is initially it can't be open the table.