I have updated in the Wiki here for Amtrak - from 3 years to 2 years. Per its updated T&C as of April 3, 2019, under "D. Point Expiration":
Subject to these Program Terms and Conditions, points earned under the Program will not expire as long as the Program continues and the Member’s Program account is active. “Active” means that the Member earns and/or redeems Program points using his or her Membership Number within a 24-month period.
https://www.amtrak.com/guestrewards/terms
The linked FT thread in the wiki had already been updated in its own wiki.