Quoting below a duplicate ticket which is maybe more clear.

Artist pages sort order inconsistent with label pages (MBS-6976)

For this let's take an example those two simultaneously released 『萬花鏡』＋『密航』 and 『胎児の夢』＋『蝶のすむ部屋』 compilations.

1. 『萬花鏡』＋『密航』 (CDSOL-0018/19) compiles 1st and 2nd album
2. 『胎児の夢』＋『蝶のすむ部屋』 (CDSOL-0020/21) compiles 3rd and 4th albums

 
Those are ordered correctly in their Solid RECORDS label page.
Where the current order (date / cat. / etc.) is enough for this.

But in the 佐井好子 (artist's release groups) and 佐井好子/releases artist pages, the order is not only inconsistent but not good.
Problem : 3rd/4th albums come before 1st/2nd.
I don't know the current sort order but it would be good to incorporate catalogue number (and bar code MBS-6975) as in label pages, in the same consistent order.

Maybe it's very niche stuff but image three singles released same day but that have a logical sequence.
Usually the catalogue numbers would also be in the correct sequence.
So i thought it would make sense to insert the first release date's first catalogue number into the RG sorting formula for display in artist overview page...

https://chatlogs.musicbrainz.org/musicbrainz-devel/2013/2013-10/2013-10-10.html#T12-40-12-670380

ocharles : « release groups are sorted by their primary type, their secondary types (in english, in alphabetical order), their first release date, and then their name
if all of those properties are equal, the sorting is random »
jesus2099 : « mmh would it be acceptable to insert first release date's first catalogue number after first release date and before name ? »
ocharles : « that could be done »