Mark, it's still not clear what is meant by "true indicated airspeed". In today's terminology, it's either "true airspeed" or "indicated airspeed". "True indicated airspeed" is a contradiction. Kind of like "real imitation crab meat".
Is there another section in the book that defines terms? Because my first thought was like
@Tspin 's, where "true indicated" means "accurately corrected indicated", which says to me "calibrated".
Or it's possible, of course, that "indicated" is an extraneous word. Or it's possible that back in 1957 the terms weren't defined the same as today. Or several other scenarios.