I'd grant you that the revolver in question, while officially designated Colt's Double Action Revolver Model 1909 was a New Service, but the ".45lc" is not strictly correct. The new revolver was adopted with a new cartridge, the Cal. .45 Revolver Ball Cartridge, Model of 1909, and while these revolvers can function with .45 Colt the two cartridges aren't interchangeable.
By way of background, the .45 service cartridge adopted for use by the Army in 1873 was in a case 1.26" long, but that was replaced in 1874 with a shorter-cased (1.11") cartridge so as to suit both Colt and S&W revolvers. Hence the .45 Colt (long) or .45 Long Colt has become the designation of that earlier longer cartridge, to differentiate it from the shorter service round. The shorter cartridge however was the service version from 1874 onward, and in 1882 was upgraded to a solid head boxer primed case with a 230 gn bullet over 28 gns black powder.
Now as is well known, the US Navy and US Army adopted .38 revolvers in 1889 and 1892 respectively, using two fairly similar versions of the .38 Long Colt. The .45 ammunition didn't completely go out of production though, and I can't agree that at the time of the Phillipine campaign "the available ammunition was old". Indeed two million rounds of .45 revolver ball were produced at Frankfort Arsenal in 1901-1902 for the Phillipines campaign. Production continued up to at least 1908, with the introduction that year of a smokeless powder load.
The 1909 cartridge was a new development however, specifically for the new 1909 Model revolver. Among other things there was concern that the thin and rather narrow rim of the older .45 cartridge might lead to extraction problems with this new revolver, so the rim of the new cartridge was made thicker and of larger diameter than the older .45 service round and indeed thicker and of larger diameter than the .45 Colt (aka .45 LC). This was also done to prevent the new cartridge being used in SAA revolvers. The case was 1.274" long, and thus of roughly of the same length as the .45 Colt, and the cartridge loaded with smokeless powder. The 250 gn bullet was rated at 725 fps muzzle velocity. The 1909 cartridge only had a very short service life though of course, and went out of production before the US entered WWI.
BTW did you know that Frankfort Arsenal also developed a "Manstopper" load for the .45 revolver cartridge between 1904-1906? It was also a direct response to the Moros, and had a jacketed hollow point bullet, with longitudinal splits in the jacket. It didn't go into service though, no doubt due to all the fuss about the similar designs the British had come out with a little earlier, and the Hague Convention which resulted.