The type of epitope defines the most appropriate recovery buffer

As mentioned above, most of currently used commercial antibodies are derived either against a bacterially expressed fragment of target protein or a synthetic peptide epitope. A standard approach used for development of a specific antibody usually means that a well-exposed surface epitope area and/or unique fragment of a protein were chosen for antibody development. However, when an antibody is prepared against a unique mutated or modified epitope, or unique epitope that differs in closely related proteins of the same family of molecules, then the choice of the epitope is rather limited, and it may be not exposed or be a part of a structure which is  present only in a mature, folded molecule.

In those cases, R-Universal may be not the best buffer, as well as standard EDTA etc. The chart below may be used to choose the most appropriate buffer for epitope recovery in relation to the type of the epitope:

This epitope is usually recognised by antibodies raised against a hydrophilic peptide or  bacterially produced fragments of a target protein. 

Discontinuous epitope requires at least some proper folding of the molecule. Antibodies to such epitopes are usually raised against native antigen, often glycosylated, or in complex with other proteins. 

Structural epitope requires proper folding of the native protein, usually with cysteine bridges being intact.

In mature protein such epitope is usually hidden. Usually antibody is raised against an immunogenic
but not highly hydrophilic peptide epitope..