I couldn't find any reference material on the 2 welds in an oblong shape. Like you I thought it was just an anomaly. On this forum yesterday, there was a buttplate shown stamped outside in. While at the CMPicon SS Saturday, I found a late SA Garandicon with a S A 12-52 barrel stamped upside down. came close to getting it but Leon convinced me on a 468,xxx with a 1-42 barrel.
The Band is legit I'm sure. Just looking for further info on markings...Harrison's didn't show this particular welds.