The Treasury Department's audit of the Internal Revenue Service's 225 employee conferences that cost taxpayers nearly $50 million might not be accurate or include all of the IRS expenses because the agency that daily demands records from taxpayers didn't supply all the receipts sought by the investigators.

In the new audit, which details lavish spending for presidential hotel suites, expensive speakers and exorbitant payments for trinkets including travel mugs and clocks, the Treasury inspector general's office said that it couldn't stand by some of the figures in the report because IRS officials didn't provide documentation.

In reviewing a costly 2010 IRS conference in Anaheim, Calif., that sparked the IG's probe, the report said, "While IRS management provided documentation showing the total final costs at $4.1 million, we could not obtain reasonable assurance that this amount represents a full and accurate accounting of the conference costs. The IRS was unable to provide documentation to support all costs associated with the conference."

For example, while the IRS established a tracking code to chart employee spending, 188 workers ignored it and they spent about $245,000, according to the audit report. Plus, the IRS said it spent $50,187 on "videos" for the conference but didn't cough up any documentation to back it up.

The IRS has promised to do a better job tracking expenses in the future, but doesn't face the fines that a taxpayer who ignores IRS demands for documentation would pay.

For the conference, the bulk of spending, $3.7 million, covered fancy lodging for IRS workers, but spending on trinkets and favors also added up. Among them: $1,165 for sticky notes; $1.534 for engraved travel mugs and clocks; $2,449 for journals; $4,500 for award plaques; $6,060 for lanyards and badges; $12,763 for folders; and $15,699 for brief bags.