OSHA has issued enforcement guidance for the fast approaching deadline to have new Hazard Communication Safety Data Sheets (SDS) in place by June 1, 2015 here. The agency is being reasonable in recognizing it's not easy to deal with mixtures received from others. The key is being able to show "reasonable diligence and good faith efforts." Have a plan to get information from upstream suppliers and document you are following the plan. OSHA will give you a break if you can show you:
(a) Developed and documented the process used to gather the necessary classification information from its upstream suppliers and the status of such efforts;
(b) Developed and documented efforts to find hazard information from alternative sources (e.g., chemical registries); [this often is hard because you don't have complete composition information on the mixtures]
(c) Provided a written account of continued dialogue with its upstream suppliers, including dated copies of all relevant written communication with its upstream suppliers;
(d) Provided a written account of continued dialogue with its distributors, including dated copies of all relevant written communication with its distributors informing them why it has been unable to comply with HCS 2012; and,
(e) Developed the course of action it will follow to make the necessary changes to SDSs and labels. [you have 6 months to create the compliant SDS once you get the information]
This isn't going away - work steadily on getting into compliance and record what you are doing.
The new SDS requirement provides more information useful to your product stewardship program and should strengthen supply chain communication, as well as being necessary for compliance.