... knowing as I do the precise location of the body dump, I find it quite easy to believe that a snow-covered body could have lain there for days in the cold weather before there was sufficient decomposition to attract the attention of a passing dog.
Welcome, Aneurin. It seems that you have a considerable advantage over the rest of us in the shape of personal knowledge. Would you venture to express your own provisional opinion of the most likely time for the body to have been dumped ?