Should we be inputting an employee's salary 'effective date' as the last time they got an increase, or the date when they are scheduled for the next upcoming increase?

If the start date of your proposal is within the next 12 months, you can use the actual effective date of 4/2023. (ex. Start date is 12/1/2024, input current salary and effective date of 4/1/2023).

If your start date is several years out, please manually inflate the salary to what is should be at that future date, and set the effective date to be consistent with that rate. (ex. Proposal start of 7/1/2026: manually inflate salary by 2 years, and set effective date to 4/1/2026).