I read this on the packet too, and then didn't buy them. Our bedrooms get down to 5* and less in Winter. Keeping bedrooms at continuous 16-20* is crazy. How did we all survive growing up?
I'm in Perth so room temp rarely gets low! At the moment its like 25+ every night

I don't expect to keep room temp at 16-20 but I find the guide helpful. The bag I have is .5 tog summer bag so the guide doesn't go low. The 2.5 tog bags have the lower temp guide.

But you gotta wonder how we all survived!! It's all a bit overdone these days IMO