The torch's description ends with "It may also be used to fuel another torch, up to a maximum of 5000 turns of light. "
The lantern's ends with "It may also be used to fuel another lantern. " , the maximum isn't indicated there but it is available to new players by looking at the flasks of oil's first line "It can be used to fuel a brass lantern with 7500 turns of light, up to a maximum of 15000 turns of light. "
I think having the lantern description mention up to how many turns you can fuel another one might be good because consistency is generally good.