If I enter a company name into the search field, I do not receive all of the patent documents which I expected to be there. Why is this?
Espacenet is designed to give one member representing a family (simple patent family aka equivalent fillings) per result. So you will receive e.g. 6 representatives of the 6 "simple families" in your result list. If you then go to the Bibliographic data of each member from your result list, you will find more family members displayed under "Also Published as".
Please be aware that a member displayed in a result list is a last added document in the database (not necessarily the last document published). So also the result list might change as soon as further patent documents are added to the database.
This is a "feature" of Espacenet and not a mistake.