Welcome to Engineers Edge paddyh!
ISO 9001 certified organizations have demonstrated that they have in-place standard operating procedures for their various business groups and departments. Ultimately, ISO 9001 is about doing business in an organized and consistent manner within the bounds of well documented procedures. Businesses without standards and procedures tend to be – well disorganized and routinely confuse themselves.
Getting back to your parts list question, in the USA we have MIL-DTL-31000 that is often mandated in government and military engineering programs where the engineering drawing package is a deliverable, as well as the end-item product. In this standard the parts list (if on the drawing face) is numbered from the bottom.
However, not all engineering drawings are required to be created to this MIL standard on the government side in the USA and most in commercial industry engineering folks could care less (and should not care either).
On the business commercial side of engineering design, I can say without hesitation after seeing, visiting, training and consulting at hundreds of companies (private and public) that parts list orientation on engineering drawings – “It Does Not Matter” what ever works best for your organization is what I and others say.
Let me go a step further and say that most organizations don’t even have the parts on the assembly drawing anymore – they have a separate assembly parts list that is controlled in an ERP and similar procurement system. This is all about running an efficient business (different conversation).
So, in summary what matters on your engineering assembly drawings is that you have a documented procedure or standard on where, how, etc. for your assembly drawing parts list (if you do) on the drawing face in a consistent manner.
Oh yes, I’m not aware of a non-military standard that dictates how parts list go on engineering assembly drawings.