Is there any compelling reason not to use exterior caulk for an interior project? Whoever installed the T&G ceiling in my living room didn't dry the lumber properly or didn't marry the pieces tight enough because there are large gaps between many of the boards. I have a case of PL caulk that I would like to use up before it goes bad.
The only really significant difference between the two is that the exterior caulk has some UV inhibitors to keep sunlight from beating it up too badly. Some also have mold inhibitors in the formula. Neither of these will hurt for an interior application. Just be sure it is paintable.
Important point, that last one. There are two basic kinds of caulk: latex and silicone. The silicone ones are for waterproofing and are NOT paintable. Latex caulks are paintable and are commonly used around not-wet areas.