Please see attached image below. Subtype Code 15, "Flush Valve w Gate Valve", does not appear on the Feature Class Tree on the right of the image.
Did you close and reopen ArcMap and then check?
Add the Feature Class to a new MXD and then check if the new one shows up...
Closing and re-opening arcmap did not help. adding the modified feature class to the mxd did work. The original feature class needs to be erased.
Could you check by open attribute table and edit any value in the subtype field , see the menu if the new value included.
add new this template by open organize templates, then New template and add all template.as the following picture.