Michael McDowell said he did not think it "by itself amounts to a severance between the two organizations."
However he said the move was important as it was "an acknowledgement, in my view, that there was a very structured link between them in the past."
The three men have always denied that they were members of the seven-man council which runs the IRA. The links between Sinn Fein and the paramilitary group have always been somewhat shadowy, though unionists generally insist the two organizations are one and the same.
McDowell's comments came amid growing anticipation that the long-awaited IRA statement on its future will be delivered this week. McGuiness flew to the United States Wednesday to brief supporters about the IRA's intentions.
Adams called on the group in April to renounce armed struggle and engage in the political process to achieve its ends.
Speaking in Belfast Tuesday, McDowell said he looked forward to the statement, but stressed that disarmament must be "down to the last bullet."