In designing a circuit using an IC coupler, how should the threshold input current be reflected?

For the IC coupler threshold input current I_FHL(I_FLH), the following factors must be taken into account: Temperature dependency, deterioration over time, and design margin. These factors shall be digitized as Dta, Dt, and α and incorporated into the design.
For details, refer to Toshiba Application Note "Basic Characteristics and Application Circuit Design of IC Couplers", section 2. 3. 4. Typical applied design
(https://toshiba.semicon-storage.com/ap-en/semiconductor/knowledge/application-note.html)