I recently published an article in Tax Notes discussing the final regulations under section 721(c). See link which is behind Tax Notes’ paywall. https://www.taxnotes.com/tax-notes-today-federal/transfer-pricing/complexity-and-confusion-cross-border-partnership-regs-finalized/2020/02/10/2c3xl?highlight=Jackel . In the article, I pointed out that the attribution example in the final regulation preamble was incorrect because there is no concept of indirect ownership through corporations in the final regulations. See part V.A. of the article at p. 944. Recently, the IRS issued a correction notice (to be published in the Federal Register on February 18, 2020) that changes the facts of the preamble example to only deal with indirect ownership through a partnership. See https://www.federalregister.gov/documents/2020/02/18/2020-02654/transfers-of-certain-property-by-us-persons-to-partnerships-with-related-foreign-partners-correction.