From what I understand, there were also massive quality issues in China, where the quality greatly varies from several factors.
Due to the massive needs for swords, mostly from the army and merchants meant that they had to be mass produced.
This led to two major factors in quality:
1. Ores were delivered to state owned manufacturies from across the empire, meaning that you get significant variances in ores.
2. Due to the large demand for fuels that can generate high temperatures, charcoal was replaced by coal as the main source of fuel for the furnaces, which adds another layer of complexities due to the impurities contained within the coal, especially with the coal coming in from different areas of the empire.
This eventually led to Chinese swords having different hardnesses for different parts of the blade, used mostly in the Tang Dynasty where the cutting edges and the tip were made of a higher hardness steel and the body of a lower hardness steel to allow the blade to have a "sharper" blade without the sword breaking on the user. It was eventually dropped because it was deemed too expensive to maintain and replace and was thought to greatly influence the Japanese in their swordmaking as most of the Chinese imports to the Japanese took place during the Tang Dynasty.