Regardless: if you look at what Billboard (as a whole) tracks, it offers a far better view of what's popular in Japan:
From the chart's inception in 2008, to December 2010, the chart combined CD single sales data from SoundScan Japan, tracking sales at physical stores across Japan, and radio airplay figures from Japan's then 32 AM and FM radio stations sourced from the Japanese company Plantech.
In December 2010, the chart was expanded to include sales from online stores, as well as sales from iTunes Japan.
From December 2013, Billboard added two additional factors to the Billboard Japan Hot 100 chart: tweets relating to songs from Twitter data collected by NTT DATA, as well as data sourced from Gracenote on the number of times a CDs has been registered as being inserted into a computer.
From December 7, 2016 onwards, Billboard Japan teamed up with GfK Japan to distribute digital sales of each track on the Hot 100 chart (between the positions of number one to number 50) to the public. The companies will distribute the sales from over 3,900 digital stores nationwide, alongside streaming services with Apple Music, Awa and Line Music, which will commence in 2017 and will be recognised as points (similar to album-equivalent sales).
Chart rankings are based on physical singles' sales. Oricon does not include download sales. In Japan, physical sales decreased sharply in the 2000s, while download sales hit three to four times the amount of single sales.
Every Monday, Oricon receives data from outlets, but data on merchandise sold through certain channels does not make it into the charts. Oricon’s rankings of record sales are therefore not completely accurate.
The Billboard Japan Hot 100 offers a far more rounded and diverse view on a groups performance, sales and popularity.