by jabarl » Mon Nov 21, 2011 9:00 pm
When the law changes. There haven't been a new federal law change that requires a modification in 2010. State posters change when state laws change.
As far as who checks, OSHA and Department of Labor (both state and federal). While they do random checks I've never heard of them just coming to check posters. They check when they are there for something else.
If you have a poster that is out of date they will warn you. You can get every one of the posters that make up the big posters free from the various state and federal department's web sites in pdf format.