Semple approach to Traditional Highland Dress

[OC Richard]

Most of the illustrations of 18th century Highland dress tend to depict soldiers or the at the higher end of the social strata. There are very few images of the lower orders. Additionally a lot of the drawings are slightly caricaturist and unrealistic. So therefore likely inaccurate.
Some may also have been drawn from memory.
Clearly not the case in the examples above.

Several accurate observations there.

As historians we have to work with what we have- once we reach the boundaries of the extant evidence we have to admit "we just don't know". (We can leave speculation to the writers of fiction.)

For Highland Dress we have oil portraits painted from life going back to the late 17th century. These were incredibly expensive, around $100,000 in today's money, and have the disadvantage of only showing the wealthy, but the advantage of being made under the watchful eye of the subject (who was also the person footing the bill, and thus almost certainly nitpicky). The artist would have been held to the highest level of accuracy at least in terms of clothing and accessories.

We have more than enough 18th century oil portraits done from life to know exactly how people dressed.

There's a group portrait of several ordinary Highland men painted from life, which shows that then, as now, the rich and the ordinary dressed more or less the same. (I can see a historian 300 years from now seeing photos of our current celebrities in baseball hats, t-shirts, and cargo shorts, and imagining that this was only the dress of the wealthy.)

Beyond those 18th century portraits there isn't much that could be taken as being reliable. We have to set aside illustrations done from the artist's imagination, political cartoons, etc.