the main limiting factor on germination is how it is stored. And the main thing that decreases germination is humidity i.e. the seed gets a little bit humid starts to germinate but stops and dies because there is no more moisture kind of like a false start.
Most of our seeds including Broccoli are stored in a humidity & temperature controlled warehouse and we remove them to our packaging facility one bag at a time.
Regarding Broccoli, we test them (standalone) for germination on a regular basis, you can see pictures on the product page where we tested them a few months ago with excellent results. Also I germinate a group mix of seeds on a weekly basis (Alfalfa, Red Clover, Radish, Fenugreek, Kale, Broccoli) and individually (Lentils red, Pea Massey Gem), meaning I will notice if there is one particular seed not germinating. Anyway when you purchase them I suggest you store them in a airtight glass jar and either use silicon satchels to catch any moisture or just put some paper towel on the top of the seeds before you close the lid. If you have large quantities then do as above but one with a large container and one with a small container for everyday use i.e. so you not opening the large one all the time.