Thank you Rupesh. The note is very informative.
I found the answer: Here is what the system is doing while creating planned orders.
A requirement can only peg to a receipt if the following preconditions are met:
- Requirement time >= receipt time + maturity time - maximum backwards edge length
(note: The maximum backward edge length is maintained in the product master under 'Latest receipt maximum ... in line with requirement'). As of SCM 3.1, the field is called 'Maximum delay of a receipt').
- Requirement time + required minimum shelf life <= receipt time + shelf life
Requirement time + required maximum shelf life >= receipt time + shelf life