I suspect that since you can knit with ribbon yarn on a wide variety of needles, that they don’t want to give you a tension number on the label. You can knit with it with super-large needles for a lacy web effect, and you can knit with more ‘normal’ sized needles for a tighter, cushier fabric.
Since the yarn is Sirdar and the pattern is Sirdar, I’d go with what the pattern says–there must be a gauge there, somewhere.