Dear Sibylle,
The definition provided by Timo and the description in the WIGOS Newsletter are not inconsistent, actually, they intend to mean the same, in complementing each others i.e.:
- if a station existed before July 2016, but was never affiliated with a WMO Programme, it was never assigned with a WMO ID, so it couldn't have previously exchanged data internationally (at least not officially).
If you have stations which are not registered in OSCAR/Surface but that existed already before 2016, with a WMO ID (internally assigned), those stations "don't exist officially", i.e. WMO is not aware of them if they were never registered in Vol.A; So, now they will have to be registered in OSCAR/Surface as "new stations".
Therefore, the stations you want to register in OSCAR/Surface should be assigned with a WSI containing your ISO country code in the 2nd block (Issuer of Identifier), including those stations that are already sending data onto GTS. The content for the 4th block, local identifier (as well as for the 3rd block, Issue number) is up to national decision, although it is a current practice to use an existing ID (either WMO or national number) in the 4th block.
I hope this helps, but please feel free to contact me directly for further clarifications if needed.
Best regards,
Luis