In December 1706 Charles XII wrote a letter to Stockholm with instructions regarding the uniforms for the new recruits which would arrive to the main army the following spring. He instructed that the lower part of the coat was to be wider with folds in the sides and back, and that there would be no buttons below the waist. The amount of cloth needed to manufacture a coat thus increased from 4½ elle to 5½ elle.
This letter has been interpreted by many as the introduction of an entirely new uniform model which then was to be in use for the remainder of the war (i.e. the Younger Karoliner Uniform). Possibly the entire Swedish main army was equipped with these new uniforms during their stay in Saxony 1706-1707 (by courtesy of the Saxon tax payers), although the older uniforms might have remained in use by some regiments until the battle of Poltava 1709. The restored regiments would then definitely have been issued the new model, even though some older regiments which had stayed at home might still have used older uniforms after 1709.
But that leads to the question of how the uniforms looked like before December 1706. A uniform coat preserved in the Army Museum has generally been regarded to be the prototype for that uniform which was presumed to have been used during the period 1687-1706 (i.e. the Older Karoliner Uniform). The starting year of 1687 is based on a letter from that year to the colonel of Älvsborg Regiment in which the king declares that henceforth all regiments were to have blue coats.
The main differences from this so called Older Karoliner Uniform (shown above) and the classic younger uniform are the absence of a collar, large cuffs, buttons along the whole front, double vertical pocket flaps and no turnbacks.
However, Lars-Eric Höglund has gradually questioned the existence of this uniform. Because other than the prototype found in the Army Museum there are no hard evidence of it to be found anywhere. Höglund noted in his first book that his research contradicted the claim of the older uniform being used until 1706. It appeared to him that it ceased to be issued ca 1692. References of horizontal pocket flaps, collars and a number of buttons that resembled the younger uniform rather than the older one led him to the conclusion that the older uniform must have been in the process of evolving into the younger uniform. So he proposed the idea of an “Intermediate Karoliner Uniform” which he dated to the period of 1694-1706.
But in his second book he wrote about a revelation when he saw an illustration of Nyland Regiment’s drummers from 1696. Their uniforms obviously did not match those that were issued to them in 1696 so logically it must be the uniforms they were issued in 1688. However, these were obviously not of the Older Karoliner type either. Instead they looked just like the uniforms of the Scanian War. With this revelation Höglund began to doubt whether the “Older Karoliner Uniform” had ever been used. After all there were no hard evidence of its existence other than the one coat in the Army Museum. What he previously had thought to be references to the Older Karoliner Uniform in his research could just as well be uniforms of the Scanian War type still in use. His conclusion was that the coat in the Army museum was most likely just a rejected prototype that never made it to the army.
What this means is that the Scanian War uniforms were replaced in the 1690s by a new uniform coat which had a collar, small cuffs, horizontal pocket flaps and about the same number of buttons as the uniform from 1706. The differences between this uniform and the so called Younger Karoliner Uniform are not that great. Other than the greater width and folds in the lower button-less part of the coat, it would only be the turnbacks which could have distinguished them. But I am not aware of any source mentioning the introduction of the turnbacks. Charles XII’s instruction in December 1706 to only have buttons down to the waist could be interpreted to be the introduction. But in a portrait from the same year the king is depicted with turnbacks, with a caption explicitly saying that this was how he was dressed when he was on campaign in 1700. Note the buttons below the waist.
And I have also seen a photo of the “Older Karoliner Uniform” prototype arranged with turnbacks, so evidently even that uniform could have been worn in such a way if that was desired.