In a direct communication, the source explained that as of 1 January 2018:

• The counties 16 Sor-Trøndelag and 17 Nord-Trøndelag were merged into 50 Trøndelag.
• The municipalities 1624 Rissa and 1718 Leksvik were merged to new municipality 5054 Indre Fosen. (Our extract does not include this geo level.)

In response, we have:

1. There is no change to our concept codes or catalog.
2. Archived the terminated counties (January 1992 to December 2017) by marking their metadata as "discontinued".
3. Created a new geo code for 50 Trøndelag.
4. Created new series using the new geo code. The new county is reported from January 2018, but we have extended it to January 1992 since it is the sum of the two predecessor counties. There is a secondary source citation to this effect.
5. This pertains to the reported NSA series (six concepts) and our SA supplements (two concepts).

The series reside in the historical catalog (Norway » Real Estate » Residential » Stage of construction » ... » Monthly) and include, for example:

• HSASTRRUM.INOR_STR = [DISCONTINUED] Real estate: Dwelling starts - Utility floor space, (Ths. m², NSA) - for South Trøndelag
• HSQCNPRUM.INOR_NTR = [DISCONTINUED] Real estate: Dwellings under construction, (#, NSA) - for North Trøndelag
• HSQCMPRUM.INOR_TRN = Real estate: Dwellings completed, (#, NSA) - for Trøndelag
• HSQCMPRAM.INOR_TRN = Real estate: Dwellings completed, (#, SAAR) - for Trøndelag

Because catalog locations are subject to change, the upper-right search box on DataBuffet.com provide a "find in catalog" mode that accepts a mnemonic.