Because lower temperature ratings and adding down have been mentioned twice, consider this ... I don't know about LL but other vendors (HG for example) have suggested that extra fill is more to prevent down shifting. Some prefer that. And extra down is sort of a security blanket. When I started out, I always added a couple of ounces more down. But being able to easily redistribute down after it has migrated is also desirable. So you do you.

Increased R factor - insulation from cold - is achieved more effectively by more loft - the cut of the UQ, not just more down. HG has said it's better to get the next warmer bag - cut for more loft - than to add more down to a bag cut for a smaller loft.

That said, certainly one vendor's 20° bag can be warmer than another's; various design choices. My UGQ 20° TQ is warmer than my HG 20° TQ. BUT the UGQ quilt has a sewn footbox. HG's cinch footbox, which I requested, allows for more venting, making it more comfortable as the nighttime temperatures warm up.

Two (maybe more) circle symbols can be used for the degree symbol on a Mac. This is Shift-Option-8 °. This is Option-k ˚
The option-k looks a little smaller and higher. Let's see how they look side by side ... 20° and 20˚. Take your pick.