I had a looksee at yours and while workable, a lot of unnecessary text seemed to garble things up.
Here's what I would suggest - create seasonal maps for every season (not necessarily every month) and then follow the template I've provided below. It is what I used for my Mount St. Helens Pre-1980 Experience package currently in final development.
You will need to copy and paste the coordinates from your template into your final working INF, as well as output file name, etc.
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[Source]
Type = MultiSource
NumberOfSources = 8
[Source1]
Type = BMP
Layer = Imagery
SourceDir = "."
SourceFile = "MSH_Pre_1980_Aerial_WI.bmp"
Variation = December,January,February
Channel_BlendMask = 7.0
Channel_LandWaterMask = 8.0
ULXMAP = -122.250521593
ULYMAP = 46.250018736
XDIM = 2.96274685329598E-05
YDIM = 2.08648226351351E-05
[Source2]
Type = BMP
Layer = Imagery
SourceDir = "."
SourceFile = "MSH_Pre_1980_Aerial_HW.bmp"
Variation = December,January
Channel_BlendMask = 7.0
Channel_LandWaterMask = 8.0
ULXMAP = -122.250521593
ULYMAP = 46.250018736
XDIM = 2.96274685329598E-05
YDIM = 2.08648226351351E-05
[Source3]
Type = BMP
Layer = Imagery
SourceDir = "."
SourceFile = "MSH_Pre_1980_Aerial_SP.bmp"
Variation = March,April,May,June
Channel_BlendMask = 7.0
Channel_LandWaterMask = 8.0
ULXMAP = -122.250521593
ULYMAP = 46.250018736
XDIM = 2.96274685329598E-05
YDIM = 2.08648226351351E-05
[Source4]
Type = BMP
Layer = Imagery
SourceDir = "."
SourceFile = "MSH_Pre_1980_Aerial_SU.bmp"
Variation = July,August,September
Channel_BlendMask = 7.0
Channel_LandWaterMask = 8.0
ULXMAP = -122.250521593
ULYMAP = 46.250018736
XDIM = 2.96274685329598E-05
YDIM = 2.08648226351351E-05
[Source5]
Type = BMP
Layer = Imagery
SourceDir = "."
SourceFile = "MSH_Pre_1980_Aerial_FA.bmp"
Variation = October,November
Channel_BlendMask = 7.0
Channel_LandWaterMask = 8.0
ULXMAP = -122.250521593
ULYMAP = 46.250018736
XDIM = 2.96274685329598E-05
YDIM = 2.08648226351351E-05
[Source6]
Type = BMP
Layer = Imagery
SourceDir = "."
SourceFile = "MSH_Pre_1980_Aerial_Night.bmp"
Variation = Night
Channel_BlendMask = 7.0
Channel_LandWaterMask = 8.0
ULXMAP = -122.250521593
ULYMAP = 46.250018736
XDIM = 2.96274685329598E-05
YDIM = 2.08648226351351E-05
[Source7]
Type = BMP
Layer = Imagery
SourceDir = "."
SourceFile = "MSH_Pre_1980_Aerial_BlendMask.bmp"
Variation = All
Channel_BlendMask = 7.0
Channel_LandWaterMask = 8.0
ULXMAP = -122.250521593
ULYMAP = 46.250018736
XDIM = 2.96274685329598E-05
YDIM = 2.08648226351351E-05
[Source8]
Type = BMP
Layer = Imagery
SourceDir = "."
SourceFile = "MSH_Pre_1980_Aerial_LWM.bmp"
Variation = All
Channel_BlendMask = 7.0
Channel_LandWaterMask = 8.0
ULXMAP = -122.250521593
ULYMAP = 46.250018736
XDIM = 2.96274685329598E-05
YDIM = 2.08648226351351E-05
[Destination]
DestDir = "."
DestBaseFileName = "MSH_Pre_1980_Aerial_Final"
DestFileType = BGL
LOD = 6,16
UseSourceDimensions = 1
CompressionQuality = 100
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