I found out the hard way that sleeping bag ratings can be just a wee bit misleading.
Once on a trip (memorial day weekend, surprise overnight temps in low 30's), I found myself freezing in my 30f bag.
Well, later, to my surprise, I found a tag with a RANGE of temps Comfort (43f), Limit (36f), extreme (7f)
My lesson learned, is to ADD @20 degrees to whatever the bag rating is, to get to my comfort zone.
If a bag is rated to say, 30f, and a night forecast of 50f, I think I'll be good, but definitely not down to the 30's.
REI member since 1979
I trust you will find this coop journal article on sleeping bag ratings useful: https://www.rei.com/blog/camp/understanding-sleeping-bag-temperature-ratings
The rating posted on your bag seems to be fairly accurate. bear in mind that several factors influence you comfort within any bag - the R rating of your padding underneath, exposure to wind, the caloric content of your last meal, your level of exertion. I find it really helps to wear a dry base layer to bed and some sort of insulating head covering when it will be really cold. Of course, your bag should be dry with the insulation well fluffed up.
yes the tag was pretty accurate, but my point offered is that a 30F labeled bag may not keep you cozy warm at 30F, all other things being equal 😉
btw, most bags DO NOT have a nice little 'range tag' like this particular NF bag. just sayin