Q:

ArcGIS key numbering labels for every feature in one layer

I would like to use key numbering when labeling specific layer.  But the tricky thing is I want to label every feature in this way. 
By default, key numbering is last option in Strategy order (source).  And there's no possibility to change it. 
Is there any workaround to force ArcMap to use key numbering for every feature? 

A:

Belated workflow here.  Assume you're working with a point layer or with centroids of your polygon/polyline in the northern hemisphere:

Calculate a latitude field if it's not already present
Export your point layer's attribute table and open it in Excel, etc. 
Sort your latitude field descending (largest [northernmost] values on top, smallest (southern) values at the end)
Add a new field named Lat_Order
Calculate =Row()-1 for each record in the dataset (data beginning on row two will have a value of 1.  This will be your key numbering label
Save the spreadsheet, and add it to the ArcMap project as a standalone table
Join the table to your point layer based on the OBJECTID field
Label based on the the Lat_Order field
Go back to the spreadsheet and grab the Lat Order and your point's name field to display the lookup list/key legend in your map

Does this help (years later)?