I have come across some scanlations of these:

Shounen Teikoku Soushuuhen 1 - Boys' Empire Special 1

Shounen Teikoku - Boys' Empire Soushuuhen 2

Boys' Empire Extra Edition

Each of these 3 things appear to contain different tables of contents and an ongoing series called "I can't stop loving you"

I will link these clean ToCs for analysis for comparison to the 9 volumes and acknowledged 14 chapters (even though I do question if we ought to call One Fun Summer chapter 1 since it occurs later)

Soushuuhen/Special 1 https://g.hitomi.la/galleries/787536/4.jpg

05 Aki-nee
17 Mizumura-san
25 Onee-chan
35 Motoki-san y Hino-san
47 Yoshino-sensei
59 Mama
71 Despues del Trabajo
72 No puedo dejar de amarte

This is the same https://g.hitomi.la/galleries/796552/004.jpg

Except insetad of the Spanish for the last 2, page 72 is "I can't stop loving you

Soushuuhen/Special 2 in Spanish https://g.hitomi.la/galleries/787546/4.jpg
*mostly untranslatedhttp://i.nhentai.net/galleries/796557/3.jpg

05 Ikki-kun
25 Papa
37 Iki-kun y Aki-nee
45 Viaje a la playa (Beach Trip)
65 I Can't Stop Loving You (no puedo dejar de amarte)

What seems to be the case, far as I can tell, is that the "Shoushuuhen" presentation is a consolidation of chapters into larger volumes initially spread across further editions.

Shoushuuhen 1 from Aki-nee to Mama was initially spread across books/chapters 1 to 3
Shoushuuhen 2 from Ikki-kun to Beach Trip was initially spread across books 4 to 6

I think this may mean that there is an as-yet-unidentified Shoushuuhen 3 which will include the contents of books 7 to 9, which would include Makoto's Determination. Living Together and Blessing.

Since they both contain "can't stop loving you", I take it that these are entirely new stories being included in these compilations, to encourage people to buy them for the new content.

So far as I can tell from these tables of contents, there does not appear to be an inclusion of the "One Fun Sunday" or "Childhood's End" stories though

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-ty