I made cookies for my website over 3 years ago (maybe 4 years ago). They were my regular vanilla sugar cookie and royal icing recipes. Since I had gone to the effort to decorate them, I didn't want to just toss them. I stacked them in a clear glass dome cake stand (not air tight). The stand was in a corner on my kitchen counter - there was light exposure. I never touched them until about 2 months ago. I decided to throw them away. They held up fine, ever so slightly lighter in color (I had used blues and white). No mold or obvious issues. I am in the desert of Southern California, we are dry (very dry - humid days are few) and run the A/C for several months.