When you are developing a new style, it is common to reference other garments of a similar style. These reference samples serve as a visual guide to how you want different elements of your design to look, fit, or be finished. You may even base your sample spec off of the measurements of a particular reference sample.
When you get your first fit sample back from your factory or samplemaker, it won’t always be an exact copy of the reference sample – even if the sample matches the spec measurements. It may look slightly different or even fit differently. The reason why the two samples which measure the same can be different is due to several things.
First, there are only so many measurements specified in the tech pack. For example, the spec sheet probably specifies the sleeve length and bicep width, but probably doesn’t specify how tall the cap height is or how long the underarm seam is. Measurements like these are often left up to the patternmaker. While the pattern that created your reference sample and the pattern that created your sample can be the same sleeve length and bicep width, they might be vastly different shapes. The curves in between the tech pack points of measure are determined by the pattern. (You can, of course, add more points of measure to your spec, but even this won’t always result in a perfect match. It is hard to spec curved areas with 100% precision.)
Another reason the two samples might differ is due to the fabric. Unless your reference sample and your sample are made from the same material, there will be differences in how the two garments will feel and fit. This is especially true for knits. The amount of stretch and compression varies so much from fabric to fabric, that two samples even made from the same pattern can feel vastly different.
A final reason could be how the fit model is wearing the garment. This is more a concern with stretchy garments but can apply to other garment types and materials as well. Different people wear their clothes slightly differently depending on their body shape and preference. For example, one person might wear their sweatpant waistbands high on the natural waist while another might prefer a slouchier look wearing the waistband at the hip. In this case, your sample and reference sample might actually be identical, they just look different on different bodies. If you tried on and took photos of your reference samples on one person or dress form and liked how they fit, it is best to fit your sample on the same person or form this way you can compare apples to apples.
All this is why it is important to fit and test the garments during the development stage. Even if the fit of your reference sample was perfect and your sample measures the same, you might need to tweak the pattern or specs in order to get the same fit you are looking for.