Grace Field House Numbering

The Numbering on the neck is a standard identification procedure for all children that come to the Grace Field House orphanages. Like animals, they are marked before they reach the farm. These marks are always on the left side of the neck and are always 5-digit numbering. Mamas and Sisters, like any other adult human in the Hierarchy of the demons, have a numbering.

Understanding and Analysis
At first glance, the numbers appear to be random, except for the fact that they all have five digits. However, by reading the numbers back and forth, they have a clear order.

All children at Grace Field House have their numbers ending with 94. Isabella and Krone both have their numbers ending with 84. With this info, it is possible to estimate a birth order.

The diagram below is organized according to the age of the characters.

Theories derived from the numbering
There is an estimate quoted in the manga that freight shipments range from 4 to 5 per year per farm plant, with one shipment approximately every 2 months. This would in turn mean that there are 5 shipments each 2 months from the entirety of Grace Field House, or 20 to 25 per year. The 20-year age gap between Isabella and her son Ray indicates that 581 children were born, and presumably shipped out, in this time, which would mean that around 30 children are born each year and in turn fits with there being 6 children of the same age each plantation until the age they can be shipped out, such as the children who were between 3 and 5 years old at the time of the escape in 2046.

Unique Identifiers
It is later revealed that this kind of 'marking' is unique to and used only inside the Grace Field House. The other 3 Premium Farms use other ways to mark the children. This differs greatly from the Factory Farms who use brands to mark their livestock.

Trivia

 * In a commentary on the 12th edition of Weekly Shonen Jump, Kaiu Shirai commented that there were people who already discovered the pattern of the reversed numbers and this surprised him.