Brand new compression garments might look short or small when they first arrive but it is an elastic garment with built in 2 way stretch, both longitudinal and transverse (circumferential) so it is not meant to resemble actual limb size.
If you have worn compression garments before you will remember the first time you saw them and thought 'will they fit?'
On first appearance, compression garments might look small compared to limb size but as the garment hasn't been worn the elasthans in the garment have yet to be stretched. The amount of stretch in the garment will vary depending on the fabric; round knits have more elasthans and therefore have more 'stretch-ability' in comparison to flat knits that have minimal stretch but maximum 'hold' (see what a flat vs round knit garment is here).
Sometimes we also see comparisons of new unworn garments to an old well used one (placing on top of each other) or laying the garment out flat next to the a measuring tape for comparison/scale to demonstrate the 'shortness' of the garment, This comparison using the 'table measure' does not allow for the stretch of the garment after it has been worn for a while, where the elasthans have softened.
The 'true' length or 'size' of a garment, can only be correctly checked using testing methodology developed by the Hohenstein Institute, and most of the manufacturers are able to replicate this testing at their own sites during and after their manufacturing processes.
The elasthans in the garment will stretch length-wise and circumferentially, adjusting to the shape of the limb and create a 'memory' i.e. the more worn the garment is, the more 'stretched' the garment will become, one of the reasons why all garments should be washed daily and eventually repplaced.