Answer:

The 2.50/60 downgrader to 1.50 makes it "unclean" as you said, Correct.
Ways to make it clean:
Update to 2.00 - Then downgrade to 1.50 using MPH Downgrader.
Use the firmware trick & make it think its v1.00 (my fave) and then upgrade to 1.50

The use of the "Official Sony Eboot" file will make all downgraded PSP's "clean" again.

The downgrader did its job, It flashed the PSP, There were still some traces of the "2.50/60" PSP that made it "unclean".

Hope this helps with your questions,

Thanks
PSPv1.00

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