But saying they already achieved it and they are in a more “advanced” stage of Marxism,
They are not saying this. The SME is still a lower stage of socialism. If you want to see their justification, you will want to read authors from China or those who cite Chinese sources. You can read Roland Boers SwCC A foreigners guide, or if you want something shorter, there was a recentish paper "Analysis of the innovation and development of the socialist market economy theory" by Jiayong Hu, just to name two.
If you want to understand china's decisions here on a longer time span, you can look into Cheng Enfu, like his book China's Economic Dialectic.
There is also this book: https://www.taylorfrancis.com/books/mono/10.4324/9781003267355/socialist-economic-development-21st-century-alberto-gabriele-elias-jabbour
They are not saying this. The SME is still a lower stage of socialism. If you want to see their justification, you will want to read authors from China or those who cite Chinese sources. You can read Roland Boers SwCC A foreigners guide, or if you want something shorter, there was a recentish paper "Analysis of the innovation and development of the socialist market economy theory" by Jiayong Hu, just to name two.
If you want to understand china's decisions here on a longer time span, you can look into Cheng Enfu, like his book China's Economic Dialectic.
There is also this book: https://www.taylorfrancis.com/books/mono/10.4324/9781003267355/socialist-economic-development-21st-century-alberto-gabriele-elias-jabbour