In a footnote to the data, the source explained:

Compared with the "indicateur rapide-série O" of 31th May 2017, the turnover index of retail trade for Luxembourg for January 2015 and the subsequent months has been revised as a result of restructuring operations in the internet sales activity branch of the Luxembourg retail trade sector. This restructuring will have an impact on other statistics.

In response, we have synchronized Data Buffet. We have not appended a notation to the series metadata, because this is not a definitional break.

The impacted series reside in the historical catalog (Luxembourg » Consumer » Retail turnover index) and include, for example: 

• WRI47AM.ILUX    = Retail trade; except of motor vehicles and motorcycles [47], (Index 2010 =100, SA)
• WRI47UM.ILUX    = Retail trade; except of motor vehicles and motorcycles [47], (Index 2010=100, NSA)
• WRIROTHRUM.ILUX = Other retail trade [47.7 to 47.9], (Index 2010=100, NSA)