It helps if you still have friends that work at the company, that can kind of spy for you too.

An older woman was fired from the company I worked at in the early 2000s, and she was friends with a few people that still worked at the company. Found out she was replaced with a younger less qualified guy, and her friends were able to corroborate a lot of the ageism/sexism stuff, and she won the suit. Think she ended up being awarded something like whatever her salary was until the age of retirement, and ended up with close to a million dollar settlement.