In the adventure the Warlock of the Stonecrowns, the Drake had contact with a drow and her corpse could be found in section 67 in the Halls of Darkness in the Bastard's Borrow. The drow corpse is found with a drow chain armor, a broken hand crossbow, and a holy symbol to Lloth. Now this is not the only oddity found in that adventure. Other such treasures the Drake has are at least seven true names of demon princes and powerful artifacts like the Midnight Cauldron, the Mother of Storms, and the Ebon Cube. Again; great adventure if you have never read it.

So if a person wants to spice things up: one could add Drow as foreign indavders like the Githzerai (if I am picking the right Gith). If the world of BR has no Drow, and Lloth loves non-drow elf followers, then it makes sense that maybe Lloth would love to gain a foot hold in BR to gain new elf followers. Adding in something and claiming it is from another plane is lazy writing that everyone loves. Toss in an adventure with a band of time traveling tinker gnomes that take the players back in time to a point where the adventures lost their horses because they stole them from themselves now in the past. Do whatever you want; it is just D&D.

side note: no orcs in BR? I like to think of Cerillia as the land of monsters and whatever made the goblins a little stronger than normal hooked the orcs of BR up and upgraded them all to Orogs. So while a classic D&D game has a variety of lose goblin bands and rather stupid orc nations: BR has several united goblin kingdoms and the more advanced Orog. I think that is fine so that BR is just not rules for domain management overlaid on a generic D&D world. No 10 basic dragons, each is unique and powerful creature of legend.