I rather suspect that over the years modelling 'stuff' has evolved to have the ability to move and hide.
I give you a recent example. When the half-track GB was suggested I dug out my Trumpeter Sd.Kfz 7/1 from the bottom of the stash in the spare bedroom. It has been there for over 10 years. I checked it over and as I knew I'd need it in October I put it on a shelf in the model room rather than back in the stash. This morning, as it was too hot to model, I thought I'd have a look at the instructions in readiness for the GB start. Now believe it or not but that kit had put itself back in the stash in the spare room. Now the wife reckons my memory is so bad that I simply forgot that I had, in fact, returned it to the stash.
I know better. That kit secretly took itself back to where it had lived for 10+ years!