Updating Project Tasks on form or in Planning Console does not take entered dates earlier than 2020 (such as 2019), and on update, dates revert to the current year. In addition, Planned Duration does not match Planned end date - Planned start date. 

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If the Planned dates will not take earlier year dates, the associated Project schedule entries have a year later than the desired year.

Example, if the desired Planned end date is in year 2001, then the associated Project schedule's Start date time (coming from the Schedule entry) should be 2000.

1. Navigate to System Scheduler > Schedules > Schedules
2. Open the Project Schedule that is set on your Project (Every Project has a schedule associated, by default, this is the Project Management Schedule)
3. In the Schedule Entries related list, make sure that the 'Start date time' has a YEAR that is before the date you wish to include in your Projects *The End date time does not influence what dates may be used in Project
4. Update 'Start date time' by either double-clicking the cell in the Related List or open each individual Schedule Entry. (Recommended: Open each individual record and update in record)