Mellotronists

It seems to me more easily explained by a big-ticket item languishing 
on a store's sales floor until the right combination of cash and 
motivated buyer walked in.  I actually own a synth that I drooled on 
for over a year in the late 70's when it resided at a small music 
store in Vermont, which somebody eventually purchased and kept for 
many years, only to sell it to me via eBay a couple of years ago - I 
know that it would exhibit the same asynchronicity of date of sale 
vs. date of manufacture as a result of sitting in that store for so 
long. (Yes, I do know it's the same one because the eBay seller 
shared the provenance with me, and it turned out that his brother 
actually replaced me in the band I was in when I was drooling over 
the instrument!)
JS