Two very powerful tables which can be used to check requirements of stock in MD04, are the tables VBBE (Sales Requirements: Individual Records) and VBBS (Sales Requirement Totals Record).
Essentially if it is not in VBBE or VBBS dont expect it to be in MD04. If you do expect it to be in MD04 you need to re-check your availability check and transfer of requirements config.
Also dont forget the report SDRQCR21. (Check oss for more info on SDRQCR21.)