Good morning, vectro. 
Thanks for catching that! The open data parcel maps that I was using to confirm addresses as I was scanning through the area only showed 529 on the lot. From ground imagery both 527 and 529 exist, but since I'm not local, it's difficult to know which building is which and assign the numbers appropriately. Additionally, since I was creating similar two-building relations (see 532 Through St and 515/539 Reed St) for single address lots in the area to avoid duplicate addresses on buildings, it’s entirely possible I just looped this lot in as well. I can add 527 to the address on the relation or break the relation up appropriately if you happen to know which building is exactly which number. 
Awaiting your response,
Arianna