We have a specific date for the invention of the Tengwar by Rúmil, some 3,075 years before the first rising of the Sun. It is not established, however, that the tehtar were part of this initial invention, and it seems very unlikely that they all appeared intact in the first iteration of the writing system. We know that the Tengwar evolved over time, most radically in their redevelopment by Fëanor, and the tehtar presumably followed a similar path of gradual adaptation and improvement.