Lindsay,
Z1.4 is typically used for “attributes” sampling, more of a go-no-go inspection, and there are several “levels' of sampling depending on consideration for the product quality history as delivered to a given Customer plus additional consideration for the significance of the defect(ives) [Critical, Major or Minor]
Z1.9 is used for sampling of ”Variables" and is generally considered more difficult to implement and manage as each characteristic of interest must be sampled and analyzed separately
If you have access to The Certified Quality Engineer's handbook [Burke and Silvestrini] there is a reasonable overview with a couple of examples. Hope this helps!
Wil