P-51D-20 to -30. Dallas tended to switch straight between production blocks, Inglewood tended to complete a couple from each new block around 4 to 5 weeks before switching production to the new standard. Dates according to the USAAF,
Dallas,
first P-51D-20-NT factory completed 8 March 1945, 13 P-51D-20-NT accepted 16 March, 8 delivered the same day.
first P-51D-25-NT factory completed 11 April 1945, accepted 20 April, delivered the same day.
first P-51D-30-NT factory completed 27 June 1945, first acceptance 17 July, delivered the same day.
Inglewood,
first P-51D-20-NA factory completed 11 September 1944, accepted 28 September, delivered 2 October, series production from late October.
first P-51D-25-NA factory completed 20 December 1944, first acceptance 9 January 1945, delivered 11 January, series production from mid February
first P-51D-25-30 factory completed 21 March 1945, first acceptance 5 April, delivered 6 April, series production from mid May
After this comes what the definition of entered service is.