Is it not possible it simply means that Tess's stock will vary every day, like Eva's or every three days like Amanda's? Same total stock just a limited number available at a time. You could spend a week waiting for that one emote you wanted to appear? I spent three months checking Eva everyday for the Winterborn Mark emblem! It was the last one i needed. Then it appears twice in three days. That could be what it means by 'less direct and predictable'. Remember the subclass emblem fuss when everyone said the emblems weren't dropping after completing the PVE quest, not realising there was a PVP quest coming? Its probably not as bad as you think. Bungie drip feeding deliberately obscure information doesn't help.