Answer: There is indeed an upper limit for God's Blade Stigma experience.
There are four types of stigmata: orange, purple, blue and green, each with levels 2 to 10, for a total of 9 levels. The amount of experience required for each level is different. For example, level 2 of Orange Stigmata requires 960 experience, while level 10 requires 76,800 experience.
The specific value of the upper limit of stigma experience has not been disclosed, but what is certain is that there is an upper limit for stigma experience, and players will be limited by experience when improving stigma.