How to catch the main point of a complicated sentence?

Hi Everyone,

I have met a sentence of UPC500(UPC500 is a document of rules and regulations which regulate the practices of related part of letter of credit ,like the bank ,the importer and the exporters.The documents are drafted by the international chamber of commerce .
The sentence is as follows.


Shipments made by post or by courier will not be regarded as partial shipments if the post receipts or certificates of posting or courier's receipts or dispatch notes appear to have been stamped, signed or otherwise authenticated in the place from which the Credit stipulates the goods are to be dispatched, and on the same date.

Is the most important point of this sentence is that the shipments will not be considered as partial shipments if receipts or certificates or notes are stamped ,signed or authenticated on the same date?

For a foreigner ,how to catch the main idea of a complicated sentence like this:-) ?

Thank you all .

I would say that the place and date are equally important here.