Not a massive shirt collector but I would guess that match worn is where the money is. From that point of view I'd guess a couple of shirts would be really worth having for their rarity.
As we only wore this 3 times, and there's been a recent version released, a match worn must be nearly impossible to get hold of
Also in the 1974-75 season we had an all blue kit. Not dark blue, but royal blue. Again it was only worn about 4 times and I've never seen one. There isn't even a colour photo of it. But it was an all blue shirt (think Chelsea) with a Blades badge on it. I remember seeing it at Stoke and thought it was very weird. This pic of Len Badger was taken at Anfield.
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