Dany,
The term "natural" used in the context of pipe tobacco is incredibly misleading.
http://pipesmagazine.com/blog/put-that-in-your-pipe/a-tale-of-two-syrups-casings-and-top-dressings/
Read the article listed above. It will explain (better than I can) the difference between casings and top dressings in pipe tobaccos.
"Aromatics" (imagine Captain Black or Old Port) are "cased" and "topped" with heavy doses of flavouring such as chocolate, vanilla, or cherry. They are designed to be sweet and to have a prominent pleasant room note.
Blends that are considered "natural" such as straight Virginias and burleys are often "cased" with a substance such as sugar, licorice, molasses, et cetera. This does not make them aromatics! It may, however, impart subtle flavouring or aroma to the blends.
I believe that the Blatter blends have a noticeable "casing" but yet the tobacconist continues to describe them as natural in sharp contrast to the "aromatic" pipe tobaccos they have available. I really don't know why they are calling them natural tobaccos, but I have my own thoughts on the subject so I can't speak for their reasoning...
Anyway, Dany, this is confusing but pipe tobaccos in general are often quite processed in comparison to the truly natural flavours of your premium hand rolled cigars.
Most English or Balkan or Oriental blends are "natural" with no added flavouring, but there are countless exceptions to that. Blatter Reserve is an English blend but from your testimony and from some of the reviews I have read it does have a noticeable casing. I really do not know what to believe without trying it for myself. Dunhill Nightcap is an example of an English blend that should have no added flavouring beyond the smokiness of latakia. Yes it tastes of campfire, earth, leather, mushrooms, et cetera, but these are functions of latakia.
Long story short, there are few pipe tobacco blends that are completely "natural" because they would be overly harsh tasting. The tobacco is cured and flavoured for optimal smoking pleasure. In most "straight" or "natural" blends the flavours are not noticeable but they add nuances to the natural tobacco taste. Samuel Gawith Full Virginia Flake and Peterson Irish Flake that I mentioned earlier would fall into this category.
Aromatics, on the other hand, are meant to showcase the added flavours.
"Crossovers" such as Frog Morton (a semi aromatic English) and possibly Blatter Reserve fall somewhere in between.
I hope I have not confused you further, but it is a fairly confusing subject.
GL Pease Union Square is the only Virginia I know of on the market that is completely unflavoured, but there are many Virginias where the flavouring/casing just serves to pleasantly highlight the characteristics of the tobacco.