Both here at https://www.mangaupdates.com/series.html?id=27211 and over at http://myanimelist.net/manga/11200/Shounen_Teikoku people say fourteen chapters...

1. One Fun Sunday
2. Aki-nee
3. Mizuhara-san
4. Onee-chan
5. Motoki-san and Hino-san
6. Yoshino-sensei
7. Mom
8. Ikki-kun
9. Dad
10. Ikki-kun and Aki-nee
11. Beach Trip
12. Makoto's Determination
13. Living Together (With the Family)
14. Blessing

This all preceding the "Childhood's End" spinoff.

I question the legitimacy of this numbering. I think there is confusion because some of the chapters contain 2 stories instead of 1, but separate stories do not make for a separate chapter.

You can clearly see on PervEden that it has 9 chapters.

"One Fun Sunday" is a chapter that features Makoto Tamura with Hitomi Mizuhara and Mina Tamura. It is clearly later in the series.

Chapter 1's cover shows Makoto Tamura and Aki Higurashi on the cover. The first half is their story, It is referred to as "Aki-nee" in the table of contents, on page 5. The second half, on page 17, is called Mizuhara-san. I think it would be okay to directly link to the ToC since it is clean:

Chapter 1 http://cdn.perveden.com/mangasimg/8e/8e0f892a452f2a3df2ffbb b1bacd1b9627e05a4c7fc58adb5eb5c4c9.jpg

Chaopter 2 http://cdn.perveden.com/mangasimg/da/da7c346481e2b42074a2 59121c597fa50faea850b66ed3cbdb5b5ab7.JPG

(reference to things on pages 5, 15 and 25)

Or is what I think is chapter 1 actually more like volume 1? Containing 2 chapters? In that case are there 9 volumes?

OFS sounds more like something that came out as a teaser, some kind of mid-story preview.

________________
-ty

The current release numbering is most likely based off of sirC's original numbering scheme on his news post for the scanlation

________________
A just ruler amongst tyrants