I did some more analysis on this issue:
- “transport association” can be identified as one of the 43 OV-concessies Nederland?
- see also NL-OV/Bus - OpenStreetMap Wiki
- “search area” can be one of the provinces
- or more (Groningen-Drenthe)
- or smaller (Stadsbus Den Haag)
- locations in the OSM wiki could start with
https://wiki.openstreetmap.org/wiki/NL-OV/PTNA/
The table on the NL page of PTNA will be organized by the Country code#ISO 3166-2 of the provinces plus the name of the ‘network’
- NL-NH-aaa
- NL-UT-bbb
- NL-ZH-zzz
- …
where ‘aaa’, ‘bbb’ and ‘zzz’ are the names of the concessies (OSM: ‘network’) in long or short form.