Most of K Street is complying fully with the lobbying disclosure laws that went into effect four years ago, a new Government Accountability Office report shows, but some lobbyists are missing forms and don’t understand some aspects of the law.

The watchdog arm of Congress found that lobbyists failed to disclose at least 2 percent of their political contributions that were documented in the Federal Election Commission database. The GAO’s findings mirror a study by CQ MoneyLine, which found at least 250 registered lobbyists — including a dozen former Members of Congress — who did not report their new lobbying campaign contributions for the first half of 2008.

Lobbyist reports that detail how much lobbyists are paid to influence Congress and federal agencies are getting better. Overall, the GAO found 97 percent of lobbyists were able to provide the GAO with documentation for reported income and expenses for most of 2010. That figure is quite a jump from 2009, when only 89 percent of the reports could be substantiated by lobbyists’ records, or 2008 when in 14 percent of cases, documentation was incomplete or contradicted federally filed reports.

However, records of the finer points of last year’s lobbying were missing in some cases. For instance, some lobbyists said they did keep records of their contacts with Congress, while others could not produce supporting documentation to show that they lobbied executive branch agencies on their reports.

The study, released Friday, notes that not all lobbyists listed for a client are necessarily working for that special interest. Several lobbyists told the GAO they listed all the firm’s lobbyists on some forms regardless of whether they were actively lobbying on behalf of that client. Other points of confusion for lobbyists included how much information to list for covered positions and the thresholds of being listed as a lobbyist.

After being contacted by the GAO, a number of lobbying groups went back to amend their filings to change the amounts reported and the name of clients, as well as to add lobbyists, bill numbers and agencies lobbied.

As of late January 2011, almost half of the nearly 1,600 lobbyists who were sent letters for noncompliance with 2008 and 2009 had corrected their lobbying reports.

The GAO’s report to Congress is required annually as part of the Honest Leadership and Open Government Act of 2007. For the report, investigators and analysts studied disclosure reports for the fourth quarter 2009 and the first three quarters of 2010.