The tube at left is clearly branded 6L5G, but has a paper tag labeling it as a 6C5.
6L5G tubes have a shiney nickel plate with no internal shielding. Most 6C5G tubes have a perforated or mesh shield as the center tube. To be fair, there is a rare form of the 6C5G made for Silvertone (pictured at right) that does not have the shield.
The 6L5G is essentially a 150mA filament version of the 6C5G, which has a 300mA filament. However, the internal shield of the 6C5G makes the output capacitances much different.