Why are generic style labels for art movements often problematic?

Throughout Art History the canon often compartmentalises different movements, which creates a lot of pressure to identify the particular ‘style’ of an artwork. Although this is a useful introductory tool to the artwork to begin your analysis, it is important to remember that parts of it may not fit with one specific label, but this does not make it any less a part of that style. For example, the ‘post-impressionist’ style. This was a group of artists who identified with the ideas of the Impressionist style, but furthered the artistic development that it promoted. However, their ideas are separate and they do not present a coherent style, for example Gauguin and Seurat are worlds apart, but both are considered ‘Post-impressionist’. It should also be noted that style labels are often discovered after the movement and often the artist is not aware of them during their practice. In terms of applying this to an A-level context, for example in an essay, there is a particular way it should be done. Although the style label/movement should be mentioned as introductory material, it should not be said that ‘the artist was working in the post-impressionist style’, for example. Instead, it would be better to frame it by saying ‘the work of the artist can be attributed to the post-impressionist movement’, as an example.