To be more precise, The_skin_by_Pongo.zip is the "heart" and the main part of the Skin, but if you only replace this file you may have problems using it with the "old" zip files.
When a bug is fixed, the changes are also made in the corresponding zip file and not just in The_skin_by_Pongo.zip file, so if "old" zip files are used, certain enhancements may have no effect.
So, the Skin is not just that file but the whole "ux" folder.
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Why Pongo when updating the Skin not just post the file The_skin_by_Pongo.zip?
Why does Pongo every time fill the ux folder with so many useless zip?
Maybe you are using the latest file The_skin_by_Pongo.zip with other zip a year ago?
I don't use this Skin, lately I'm just doing tests, but I just tell you that the speedcam.zip file in the last 3 updates they are each different from the other, and not just because the icons and categories have changed, and the next one will still be different.
Don't do so much the "know-it-all", on the forum there are not only "experts", indeed many users know little iGO so your answers must be clear and complete, if they had been that way I would not have intervened.