One of the most important things you can do for a client as a Social Security disability lawyer is to request reopening of a prior claim. In my opinion, the issue of reopening does not get enough attention.
Reopening a prior claim can add substantially to the retroactive benefits payable to your client. At a recent hearing of mine, the judge agreed (based upon new and material evidence) to reopen an SSI claim filed 22 months prior to the current claim. That is a welcome lagniappe for an SSI claimant.
A prior claim may be reopened within 12 months for any reason. The 12 month period runs from the date of the initial denial of the prior claim.
A prior Social Security disability claim can be reopened within 4 years if there is good cause. An SSI claim can be reopened within 2 years for good cause. In most cases, "new and material" evidence is the basis for a finding of good cause. The 2-year and 4-year time periods run from the date of the initial determination of the prior claim.
As a lawyer, you must check with the SSA for prior claims. You should not rely on the client for this information.