Went outside to add another electrical circuit at the BBQ and
discovered that all of my nice wire-tagging had faded to non-readable.

Didn't you use the appropriate colored wires?

And as to why they didn't last you don't give us enough details.
There are different grades of receptacles. Plus being put outdoors
certainly does not help. I have no idea how good the housing is and
if it leaks. Plus I have no idea if the GFCI's that broke were cheap
ones made in China.