So what would "I go skiing in December" mean in your opinion? I read this as "I go skiing every December". Next December would be "I'm going skiing in December

So what would "I go skiing in December" mean in your opinion? I read this as "I go skiing every December". Next December would be "I'm going skiing in December", last December "I went skiing in December". When it comes to "were any mammoths still alive in December" the only logically sensible reading is "were any mammoths still alive in any December" to which the answer of course is "yes".