Logan and his corps were definitely present for the Grand Review of the Armies held in Washington DC on May 23-24, 1865. During this event, about 145,000 men (including Logan) were under the overall command of General Sherman. Many of the regiments who were with Logan that visited Mount Vernon arrived after the Grand Review before returning to their home states.
“If they are indeed corps badges,” said Pecoraro, “my educated guess of working with the evidence that we have is that they were carved by members of the 20th corps. The 20th corps was part of Sherman’s Army, as was Logan’s 15th, and perhaps oral history was conflated to combine the two. The 60th and 102nd New York regiments both visited Mount Vernon, both were in the 20th corps, served with Logan, and participated in the Grand Review.”
“As a compelling case for the 102nd [corps], before the regiment was mustered out, members of the 184th New York were transferred to it; the 184th had been part of the 6th corps (Greek Cross)," he continued. “The 102nd was in service and stationed in Alexandria at the war’s end before the men were sent home to New York in July of 1865. Therefore, it seems logical to me why you might see the star and cross together, and perhaps were carved by the 102nd as it would have included men who served in both corps.”