SD1 no stock.
SD2 fixed stock.
SD3 sliding stock.
SD4 no stock and 3 round burst.
SD5 fixed stock and 3 round burst.
SD6 sliding stock and 3 round burst.
Looking at both of your MP5's it seems that neither have a three round burst function on the selector switch. Therefore Snipermans is and SD2 and Alphabravo's is an SD3.
Your correct, BUT ours have a navy type lower reciever thats why the names are different.
Take the "K" away and you get what I got to touch quite often during my mil service.
The G36 has to be the best modern assault rifle in the world. Easy to maintain, accurate and lightweight.
H&K has topped there G36 design with the 416. Amazing rifle( check youtube for videos)