Can't imagine they get lost all that often, I would probably have one of you hadn't found one on eBay
No, guess not. It was simply me not being organised enough when stripping the engine. And paying the price for my lack of thought.
I'm also in the middle of stripping a motorcycle engine at present (a Yamaha RD350LC), and I've been religiously bagging items in resealable freezer bags of various sizes as I dismantle various sections of the engine. It does help that bike engines and components are much smaller than car engines, of course. A complete bike (wet) clutch will comfortably fit inside a medium size freezer bag. But bagging parts up as you go does seem to be a good idea to me.