In case it is not clear, the folks at BuffaloResearch do not own any city directories. Instead, we watch for when various providers digitize them. Then we collect the links here. Everything below is online in full text for free, though FamilySearch may require you to register for a free account.
Directories are shown one year per row. Some years have been digitized by more than one provider. Some years have not been digitized at all. Most directories newer than 1924 are still protected by copyright, which is why they are not online via these providers.
The Address Books are limited to upper-income households, as are the Blue Books and Social Registers.