OK, so there is a fairly comprehensive web site on Lithuanian cookery at:
There is a recipe for black rye bread, similar to my grandma's, at:
I wonder if this is the same recipe from the cookbook that I used? I wonder how it compares? This might just be the year to find out! I did have some excellent bread in Lithuania (I believe at Cili Kaimas restaurant in Vilnius) which tasted almost exactly like hers: soft, semi-dense but very uniform texture; thin, hard, black crust, delicious!
I do remember that last year, it turned out abysmal when I followed the cookbook recipe.