Do not worry about slight variations of pKa and pKb values that figure in the literature because this is not so important.
Besides, measurement of these values for strong acids and bases, is not convenient because the Henderson-Hasselbach equation is not very accurate in this case.
In case of multibasic acids and polyamines, the Henderson-Hasselbach is not applicable at all and thus, pKa and pKb are indirectly measured by other methods, e.g. monoesterification, selective monoketimination, selective monoamidation or calculative methods, e.g. Hammet equation.