Thank for looking over your carbine in a little more detail; so far, you have checked virtually ALL the boxes I suggested in my message above, and the markings match right down to the letter, don't they! Absolutely everything you have looked at indicates that you have a really pristine, unmolested carbine in as-issued condition, and the icing on the cake will be when you complete the puzzle and fill in the remaining few blanks regarding the internal components after a simple no-tools field strip. But if you have the handguard off, disassembling the remaining internal parts to see markings on slide and bolt is just a few moments away. You can already see the marking on the trigger housing, hammer and probably the sear. From what you've said so far, I'll bet they match the markings I suggested previously - a great omen!