I bought an enamel Wolfgang Puck dutch oven probably around 12 years ago - mine didn't fare as well as yours, though. I used it a lot, took pretty good care of it, but the enamel started chipping. I got it new, but at a discount store, so who knows why it ended up there (no clear damage or defects when new).

I've had similar issues with some other enameled pots I bought used, but then have others that have patina but no chips at all.

I think the quality of the coating is what really varies from brand to brand.