Is inclusion of cassette wall deposits a recommendation, or an enforceable requirement?

As of August 2013, this varies by agency, however it is projected that in due time all agencies will make it mandatory as standards get updated. NIOSH has begun by publically making this a recommendation, and has indicated they are starting the process of revising the 30+ methods affected by this recommendation. For sampling to OSHA standards compliance, accounting for cassette wall deposits is already mandatory for metals analysis. Standards agencies ASTM and ISO are also in the process of adding this requirement to their standards.