The statistics say there are 1.5 million adopted children in America, 140,000 annual adoptions, over 7 million adult adoptees and that China is the leading partnership in international adoptions. Facts about adoption are easy to come by in the form of statistics gathered by government organizations, but not all are necessarily exact. International adoptions are counted by the issuance of orphan visas to children, which may not be exact. U.S. Census data is provided on a voluntary basis. Private adopters are not required to report their adoptions. The only U.S. adoption numbers that can be trusted are those recorded by the foster system, which while a huge part of the adoption community is not representative of the whole.
Certain facts can be taken as unwritten rules. For example, traditional adopters, like married couples, are prioritized over nontraditional adopters in almost all adoption scenarios. Nontraditional adopters are more likely to be placed with a child with special needs, while not a lawful fact is still true.
Laws that govern adoption are perhaps the closest thing what universalizes such a customized process. Federal law requires all prospective adopters to pass a home study and may also provide subsidies to adoptees, but every state makes its own adoption laws as well. For example, Florida bans gay and lesbian adoption while 21 other states are open to it.