I think I managed to sort this out myself. I'm assuming that when I add a product, it's details are saved in the database and on the next auto newsletter, they all get sent in one batch, the batch of details are erased and the cycle begins again for the next auto newsletter. You could also interpret that as new products are added, a new auto newsletter is triggered there and then. I am assuming the former due to testing which would not have been necessary at this stage if this distinction was made in the docs.
A SCREENSHOT WITHOUT EXPLANATION IS NOT DOCUMENTATION!
What it is, is lazy.
It might be elementary to the devs who write the software but it isn't to a 55 year old engineer who does not do this for a living.