about discontinued parts

Hi,gurus:

I want to use discontinued parts for material replacement.

material master:Discontin. ind.=3,Individual/coll.=2

BOM:Discont. group=D1 for the material which wants to be replaced A

Follow-up group=D1 for the successive material B

but after run MD41 for the finished product,the stock of the B has not been considered,so PR for A generated

But,if i set material master:Discontin. ind.=1,Eff.-out=2008-08-08,Follow-up matl=B,Individual/coll.=

after run MD41,it'sok, the stock of the B has been considered.that's what i want.

can anyone give me some advice,thanks in advance.