Define Projections for layers with multiple locations in MXD's

    # Script to use Layers in MXD source file paths to locate and redefine projections

import arcpy, glob, os, sys, arcgisscripting

mxd = arcpy.mapping.MapDocument("N:MXDs_ThomaKLMXD GPS ValvesGPS_Shapefile_Paths.mxd")

for lyr in arcpy.mapping.ListLayers(mxd):
    if lyr.supports("DATASOURCE"):
        print lyr.dataSource

from arcpy import env, mapping
path = lyr.dataSource
env.workspace = path
env.overwriteOutput = True

print 'Reading files from ' + path

sr = arcpy.SpatialReference(103133)

x=0
z=x+1
NoProjCount=0
FileList= arcpy.mapping.ListLayers(lyr)
for lyr in FileList:
    desc = arcpy.Describe(lyr)
    SR = desc.spatialReference
    if SR.name == "Unknown":
        print "Projection of " + str(lyr) + " is " + SR.name + " so defining projection."
        f = open('NoProjection.txt', 'a')
        f.write(str(lyr)+"n")
        f.close()
        arcpy.DefineProjection_management(lyr, sr) 
        NoProjCount=NoProjCount+1
    else:    
        print lyr + " is projected " + str(SR.name)

so I have a script that works, but it only defines the projection for the very last Layer in the MXD and not the entire list of layers (there are around 50). I can tell I am missing something but I am not sure what. below is what the NoProjection.txt file has stored in it.

Valves.shp GPS PointsDataCollectedLater-ValvesValve_GPS Points GPS
PointsDataCollectedLater-ValvesValve_GPS Points GPS
PointsDataCollectedLater-ValvesValve_GPS Points GPS
PointsDataCollectedLater-ValvesValve_GPS Points GPS
PointsDataCollectedLater-ValvesValve_GPS Points GPS
PointsDataCollectedLater-ValvesValve_GPS Points GPS
PointsDataCollectedLater-ValvesValve_GPS Points GPS
PointsDataCollectedLater-ValvesValve_GPS Points