What robust intra-country inequality datasets exist for tax-evasion adjustments?

[VictoriaS]

I'm an economics student working on a thesis that challenges the common narrative of steadily decreasing global inequality, focusing instead on the divergence within nations even as cross-country gaps narrow. I'm analyzing data on wealth concentration versus income growth for the bottom 50% in both developed and developing economies over the last two decades. For researchers familiar with this area, what are the most robust contemporary datasets for tracking intra-country inequality trends, and how do you account for factors like tax evasion and offshore wealth that might significantly understate the true level of disparity in standard Gini coefficient measurements?