My 1600 f/l, like a few others, the DVLA has the capacity as 1592 (the pre f/l value), guess when registered they just carried on with the engine as being 'generic Lancia 1600'. An old phrase comes to mind, 'close enough for government work'......
It could of course have been laziness on the dealers, just copying the previous car details when first registering them.
Peter