How long can rye bread last?
While legal specifics vary from place to place, the "best before" on a product is often a requirement, but exactly what it is is left up to the manufacturer.  In other words, they have to provide one, but it can be anything they want (there may be rules about guaranteeing nutritional content for the duration, if that is subject to degradation).  So presumably they want to make it as long as possible, but not too long, because they need to discourage distributors from distributing and consumers from purchasing product which will tarnish the image of their brand.

With bread there are probably three concerns about degradation: drying out, getting stale, and going moldy.


  Is this normal "behaviour" for rye bread?


Pure rye breads are made with a sourdough starter and no wheat, so they do not rise to the same extent as normal bread.  This is part of why they are more dense and moist. I think the "high gluten flour" ingredient in yours implies it is not pure rye, but it probably still has this advantage over pure wheat.  Dense, moist breads stay moist longer versus light, dry breads -- although on the other hand, lighter breads go stale more slowly.1

But more importantly, the sourdough starter is what provides most of the leavening in a pure rye bread, not normal yeast.  Sourdough is pre-fermented and acidic, which discourages foreign bacteria and mold from taking hold -- i.e, it is a natural preservative.  It is also not an insignificant part of the bread's mass, and the flour in the sourdough starter has undergone chemical changes which make it less likely to give up the water with which it was combined -- hence sourdough based breads are considered to have a longer shelf life than any other bread.


  is this reliant on cooler North American climates


Rye is a northern grain, which is why rye bread is associated with northern cultures.  However, I think the logic of rye flour + sourdough starter will hold regardless of climate.



1. Staling, a gradual hardening, is not the same thing as drying, since moist bread may become stale (and attempts to keep bread moist will not prevent staling). Also, stale bread may be made less stale by heating it.  This is because "staleness" is actually a crystallization in the starches.