سَجَّلَ الْمُشْرِفُ الْمُلَاحَظَاتِ بِتَوَارِيخِهَا.
The supervisor recorded the observations with their dates.
The core statement is complete without bi-tawārīkhihā, yet that qualifier contributes an independent benefit: the records become easier to verify and compare over time. If it does not chiefly prevent a likely mistaken inference, tatmīm is the better analysis.
Both tatmīm and iḥtirās add wording. The former enriches a complete expression with a useful detail; the latter specifically protects the intended meaning against a plausible misreading.