Well. I do understand, that the neolithic era beeswax should be the same as the modern one, but what's about paraffin then? The modern paraffin making technology must be superior over that of 1920's. Not to mention that paraffin is not the only known material for candles (Stearin, for example, is still popular).

Similarly, the beeswax treatment technology could be improved over years too. I doubt that the above mentioned http://www.philoxia.com/survival.htm employs any nuns to hand sculpture and enchant for slower burning times their survival candles

Also, I believe that 13% is not much, because it's below the mean deviation of burning times stated for that same beeswax survival candles from www.philoxia.com : "SC72 80-100 hours". Too many factors could affect the real numbers.