The IRS has issued Revenue Ruling 2023-08, which obsoletes Revenue Ruling 58-74. Revenue Ruling 58-74 allowed taxpayers to file a claim for refund or amended return to deduct research or experimental expenditures that for prior taxable years the taxpayer had failed to deduct and for which the expense method under former § 174(a) was applicable. Revenue Ruling 2023-18 also provides transition r…