Unused New York City Subway service labels

The New York City Subway currently uses various letters and numbers to designate the routes that trains use over the differing lines in the system.

Two-digit numbers have never been used by the A Division, but have been seen on the current rollsigns of some trains, paired with colors used with other services.

It is likely that these were assigned arbitrarily, for use if the MTA changed the additional rush hour express service designators from a "diamond" version of the regular number to a separate number.

Two-digit bullets include: Trains of the B Division use single letters of the English alphabet.

[1] The letters H, K, and V can be seen on the rollsigns of some older model subway cars, with colors paired to the last primary trunk line they were assigned to.