WHY NO DIMPLES ON A ROMY RPK RECEIVER?

i see nds romy rpk receiver has no magwell dimples,why?i have pics of romy rpk with magwel dimples.was there a cutoff year?i saw a russian rpk without mag well dimples.does anyone know why the difference?the top kit is a romy rpk with dimples.
http://i41.photobucket.com/albums/e266/bigmegina/800px-Rpk_1.jpg
http://i41.photobucket.com/albums/e266/bigmegina/00-6-24-06-0047.jpg
http://i41.photobucket.com/albums/e266/bigmegina/00-6-24-06-0024.jpg

There is a cut off year, but I'm not certain of it. The dimple-less receivers have a plate spotwelded inside of it that does basically the same job. Here is a pic of a Romainain RPK that my friend took in Iraq. It has no dimples.

http://i6.photobucket.com/albums/y208/kracken/rpkclose.jpg

http://i6.photobucket.com/albums/y208/kracken/rpkatgate.jpg

. The dimple-less receivers have a plate spotwelded inside of it that does basically the same job. Here is a pic of a Romainain RPK that my friend took in Iraq. It has no dimples.

[]Just like the Century Arms ones, but the wood in nicer.

i was told that in 1972 the russians and romainians stopped using dimples.