Welcome. Merry Christmas to you as well.
Good question as to why the plating would disintegrate?? I know on my older gun's frame rails, the color is a tad darker where metal greets metal. But, the rest of the rail remains silver colored.
I just bought a US made G19C g4. I have not fired it yet. But, I will be watching it now to see what it does. I have other gen 4 Glocks and do not recall any doing that. I suppose, as long as the base metal, whatever it is, remains intact, there should not be a issue, but, as well, I'm no metallurgist either. It would seem the coating would benefit lubrication since it is one of the areas metal meets metal.
Anyhow, if it is a issue, I'm quiet sure Glock will replace it for you.
Happy New Year!!
Tim in Texas