Unless a blender has changed the recipe or his method of manufacture, it's highly unlikely that any batch is much different, one to another. But in fact, blenders usually don't admit to such changes, and in the past Samuel Gawith has been guilty of this. For awhile around 2007, 1792 was not full-bodied. Bracken Flake was stable until about this time but then they started making something totally different, a throwback of two BF generations.
The widely reported Lakeland essence does adhere to some of the Kendal blends that are are described as not topped. I taste it on Dark
Flake and Plug from time to time, but only on the first light.
I've gone through a half-dozen new tobaccos and felt they were flat for the entire contents of a tin. But if I put the tobacco down for a few months, I often get much better results.