CDJapan's own ranking doesn't mean much. What actually matters is Oricon's.
http://www.jpopasia.com/charts/jpop/oricon/
They made #22 in week 15 but dropped out of top 30 in the following week. Unfortunately, they're not anywhere in the charts for the month of April.
You should poke around in this chart next time if you really want to see how your favorite artists are faring.
http://www.oricon.co.jp/rank/
If you can't read Japanese, the top link on the left is CD Singles followed by CD Album. Pelo would be a single. After that, the inner links are daily, weekly, monthly, and annually.
I think granatnik and others here fairly well understand
that the linked CD Japan charts is only about what
is best selling in the CD Japan export chart and doesn't reflect
the total physical sales ranking. it only shows that the Pelo
single did well in export sales ranking.
Oricon is not accurate either as I explained in a post
earlier here in the thread.
They don't record all stores physical sales and
not sales of physical units done at events.
I'm not 100% sure if they have all export sales
included in their ranking. As Pelo was released
also as a international version. The Oricon chart
seem to only have the version that was release in
Japan.
Biggest reason why the singles sales ranking of Oricon
isn't accurate is because they don't so far include digital sales
of singles. And the physical unit sales have been declining
for many years now in Japan while the digital sales are
increasing.
The oricon links you provide are the physical CD single ranking.
There is only a digital album sales ranking on Oricon.
Haven't been able to find any ranking for how well Pelo
did in digital sales. I only know from posts on twitter that
it was places number one at Itunes during release as the
most sold Japanese artist single outside Japan.
One more thing. Oricon don't include the ranking of how
many times a music video is watched on youtube and others
sites.
So its hard to exactly know how well Pelo single did
in sales.
How well a idol group is doing is also these days reflected how
well they do live and how much merchandise they sell. As those
have become more important when the sales of physical CD are
dropping.
I guess they do well still as otherwise the major label wouldn't invest
in Rei and Rie like they do.
Anyway...some of us can read Japanese. Well I'm not superior at
it yet as I'm still learning