Hi GS,
There is no need to create STO for one year at DC. You should set up Spl proc type 40 & just let MRP Create Stock Transport Purchase Req . This way changes to demand /Sales order/Forecast consumption at DC will drive adjust Stock Transport Purchase Req. PR are subject to auto adjustment by MRP & hence changes in demand will change Stock Transport Purchase Req. These PR will create demand elements at Mfg plant, so there will be no need to adjust anything at Mfg plant level.
with above ,long lead time items will be taken care of. System will always address all dependent requirement based on need date. Essentially , if you enter forecast for finsihed goods for 1 year, it will generate PR in the system with release date for 1 year+ lead time.
Hope it helps,
Jatin