2020 Lobbying Disclosure: Observations on Lobbyists' Compliance with Disclosure Requirements, Report to Congressional Committees [open pdf - 1MB]
From the Highlights: "The LDA [Lobbying Disclosure Act], as amended, requires lobbyists to file quarterly disclosure reports and semiannual reports on certain political contributions. The law also includes a provision for GAO [Government Accountability Office] to annually audit lobbyists' compliance with the LDA. This report (1) determines the extent to which lobbyists can demonstrate compliance with disclosure requirements, (2) identifies challenges or potential improvements to compliance that lobbyists report, and (3) describes the efforts of USAO [U.S. Attorney's Office for the District of Columbia] in enforcing LDA compliance. This is GAO's 14th annual report under the provision."
Government Accountability Office: http://www.gao.gov/