Cleaning old 640x480 AVI clips

[Selur]

No clue what you understand under "dynamic range".
Comparing 'MVI_5394.AVI' with 'MVI_5394 Hybrid FFV1.mkv' in vsViewer using:

# Imports
import vapoursynth as vs
# getting Vapoursynth core
core = vs.core
# Loading Plugins
core.std.LoadPlugin(path="F:/Hybrid/64bit/vsfilters/SourceFilter/LSmashSource/vslsmashsource.dll")
core.std.LoadPlugin(path="F:/Hybrid/64bit/vsfilters/Support/libhistogram.dll")
# source: 'C:\Users\Selur\Desktop\MVI_5394 Hybrid FFV1.mkv'
# current color space: YUV420P8, bit depth: 8, resolution: 640x480, fps: 30, scanorder: progressive, yuv luminance scale: full, matrix: 470bg
# Loading C:\Users\Selur\Desktop\MVI_5394 Hybrid FFV1.mkv using LWLibavSource
clip1 = core.lsmas.LWLibavSource(source="C:/Users/Selur/Desktop/MVI_5394.AVI", format="YUV420P8", stream_index=0, cache=0, prefer_hw=0)
clip1 = core.hist.Levels(clip=clip1)
clip2 = core.lsmas.LWLibavSource(source="C:/Users/Selur/Desktop/MVI_5394 Hybrid FFV1.mkv", format="YUV420P8", stream_index=0, cache=0, prefer_hw=0)
clip2 = core.hist.Levels(clip=clip2)
clip = core.std.StackHorizontal([clip1, clip2])
# Output
clip.set_output()

I don't see the problem:

the levels seem to be identical.
Same when using:

# Imports
import vapoursynth as vs
# getting Vapoursynth core
core = vs.core
# Loading Plugins
core.std.LoadPlugin(path="F:/Hybrid/64bit/vsfilters/SourceFilter/LSmashSource/vslsmashsource.dll")
core.std.LoadPlugin(path="F:/Hybrid/64bit/vsfilters/Support/libhistogram.dll")
# source: 'C:\Users\Selur\Desktop\MVI_5394 Hybrid FFV1.mkv'
# current color space: YUV420P8, bit depth: 8, resolution: 640x480, fps: 30, scanorder: progressive, yuv luminance scale: full, matrix: 470bg
# Loading C:\Users\Selur\Desktop\MVI_5394 Hybrid FFV1.mkv using LWLibavSource
clip1 = core.lsmas.LWLibavSource(source="C:/Users/Selur/Desktop/MVI_5394.AVI", format="YUV420P8", stream_index=0, cache=0, prefer_hw=0)
#clip1 = core.hist.Levels(clip=clip1)
clip1 = core.hist.Color2(clip=clip1)
clip2 = core.lsmas.LWLibavSource(source="C:/Users/Selur/Desktop/MVI_5394 Hybrid FFV1.mkv", format="YUV420P8", stream_index=0, cache=0, prefer_hw=0)
#clip2 = core.hist.Levels(clip=clip2)
clip2 = core.hist.Color2(clip=clip2)
clip = core.std.StackHorizontal([clip1, clip2])
# Output
clip.set_output()

=> atm. it seems like a problem with your comparison method.
Wild guess: Could be that whatever you use during the comparison might not respect "luminance scale: full", but assue luminance scale: limited.

Cu Selur