The figures can definitely be used up until 1872 when the new uniform regulations came out.
However, troops with a sack coat and either a hat or kepi (not forage cap) could still be used up until about 1898 or so.
The US Army kept the sack coat (fatigue blouse) slightly modifying the design to have a square/pointed lay down collar instead of the more rounded collar of the 1852/55 model, and also using 5 buttons instead of 4. But at this scale, you'd be hard pressed to tell the difference.
In 1872, haversacks and canteen covers became tan canvas material, both with a grey or black "US" stencil. Most troops abandoned the knapsack as well and went with a blanket roll, with the white canvas shelter half on the outside.
Carriage/limer/etc colors remained the same.
The thing to remember is that the US Quartermaster went to great lengths to "use up" remaining ACW clothing and equipmnents in stock prior to issuing the new pattern clothing and gear in 1873. Thus, you find Custer's men using the older pattern McClellan saddles, plus cartridge boxes, belts, etc, modified for the new cartridges, at the Little Big Horn. Many of the infantry in Terry's column as well were using ACW pattern equipment, again modified for the 45/70 cartridges of the new weapons, etc.
