Hi NT Bregman,
In response to your question regarding EN standards, I manage the external standards at my organization, so I am well aware of your confusion. EN standards are European Norms (standards) created by or adopted by CEN. When they become official (published the European Journal Eurlex), member states have up to 9 months to adopt them; hence, the DIN EN, BS EN, SS EN, etc. Once the standards become official, they are no longer available for purchase as simply EN standards (and I am not certain that they are available for purchase at all until they have been adopted and published by a member state).
Regarding the differences, if the standard is a harmonized ISO standard (e.g., EN ISO 13485), the content of the adopted standard does not change (only ISO can change the primary content because ISO owns the standard), but changes can be made to the foreward and informational annexes that are added to demonstrate compliance to the Medical Device Directives (this is what 'harmonizes' standards). This is why the publication dates can be different between an ISO original standard and an adopted standard.
To ensure that we have current standards at our company, we subscribe to a standards subscription service and a standards tracking service. When populating our subscription portal, I make sure that we include the harmonized adoption of any standard that we require.
If you really want to learn more about the whole process of origination and adoption, do a Goolge search for the CENELEC Standards Primer--it's a great and informative read. It will answer most of your questions and then some.