As for the ejector rod shroud shape compare from the right side, you will see the 19-3 has sharper angles and is slightly elongated where it meets the barrel, also the blending down of their shrouds raised ribs will appear very different, Usually the later guns rib blending looks a bit smoother but these vary from gun to gun .
( on a side note the early pre 27's have the same appearance as the early pre 19's ).
One more thing I have noticed the amount of rod pin protrusion out the front of the shroud is usually more pronounced on earlier guns, I wondered if the newer ejector rod shrouds are a few mm's longer but am too lazy to measure lol.
Can you post a pic of you two guns showing their right sides, and their ejector rod pin protrusion at the front?
You should easily see the differences.