C1/C2 Common Collation

C1/C2 common collation [1] is a method of further splitting up the two sheets used in sets with 101 commons and 11 × 11 sheets. This method is used for most modern US printed sets with 101 commons.

Each sheet is split up into a run of 66 cards and a run of 55 cards. (I don't have any direct evidence of how this split related to the sheet, but given lots of prior examples of splitting sheets into the top 6 rows and bottom 5 rows, that seems likely here as well.) From the 60-card sheet, this gives a run with 33 cards each appearing twice, called A, and a run with 27 cards each appearing twice plus the short-printed card, called C1. The other sheet gives a run with 22 cards each appearing three times, called B, and a run with 18 cards each appearing three times plus the short-printed card, called C2.

Each pack will contain cards from A followed by cards from B followed by either cards from C1 or C2. Half of packs have C1 cards and half have C2 cards. C1 packs generally have 2-3 A card, 2 B cards, and 5-6 C cards. C2 packs generally have 4 A cards, 2-4 B cards, and 2-4 C cards. The possible configurations may depend on the set, however.

Typically, the cards in the A run are mono-colored cards of three particular colors (the exact choice of which may vary from set to set) in an alternating pattern. The cards in the B run are alternating mono-colored cards of the other two colors. This helps ensure that each pack is likely to have a mono-colored common of every color.

[1] This method of collation was discovered by user Medussa on the MTG Salvation forums.