Material documents and items

Hi I wanted to clarify some open questions that I have on material documents (MKPF) and Material Document Items (MSEG).

The scenario is as follows:

Last week we filled some statistical setup tables for BW extraction. The setup tables are for stock initialization (transaction MCNB) and there movements (transaction OLI1BW).

We have noticed that we have some missing Material documents and items.

We plan to load these be specifying the material documents on transaction OLI1BW.

What I am not clear on is whether material documents change and if so how - if there is a help link or info otherwise that would be helpful

Thanks