Additionally, the CMP hasn't always been in the business of re-barreling and putting together Garands out of their parts stock.
Back in the 2011 timeframe, they acquired a metric-ton of drill rifles, which were basically functional Garand parts kits less the welded-up barrels and receivers. They also previously had a pretty big stock of Garand receivers from the batch of returns from Greece circa 2005 that had finish issues and surface pitting, etc.
When the Garand stock started getting thin, they began putting together functional rifles out of all the parts with new barrels (e.g. the CMP Special Grades).
Once they started playing with headspace, they needed to test fire.