In its many embodiments, the present invention provides certain iminothiadiazine dioxide compounds, including compounds Formula (a) and include tautomers, solvates, prodrugs, esters, and deuterates thereof, and pharmaceutically acceptable salts of said compounds, tautomers, solvates, prodrugs, esters, and deuterates, wherein each of R1, R2, R3, R4, R5, R9, ring A, ring B, ring C, m, n, p, q, -L1-, -L2-, L3-, and L4- is selected independently and as defined herein. The compounds of the invention have, surprisingly and advantageously, improved solution stability. Pharmaceutical compositions comprising one or more such compounds (alone and in combination with one or more other active agents), and methods for their preparation and use in treating pathologies associated with amyloid beta (Aβ) protein, including Alzheimers Disease, are also disclosed.