scanning – Do negatives degrade resolution over time?

I've got a bunch of old negatives (~ 30 years old) that I've recently sent to a digital imaging treatment shop. It was said that the scanning resolution was slightly above 3000 dpi. I do not have any type of equipment to do it myself and I deal with a local company.

However, when the scans came back, I was surprised to discover that many of the pictures were more blurry than I remembered. I went back and found old backups that I had forgotten, some almost 20 years old, containing some of the same images that had been scanned from prints, most of time of 4×6 order. To my surprise, some of these images showed more detail in a lower resolution. For example, one of the negatives scanned to get an image of about 3100×1900, while that of the scanned 2100×1600 only print displays blurry or fuzzy details. Yet this is not so all my images On some images, the negative analysis shows more details in which I can (for example) read text that my print analysis can not even solve.

These results surprise me. I'm waiting for color changes, dust, scratches, that kind of thing, but no blur. I do not know if I should complain to the scanning service or ask for a partial refund and try somewhere else (I've had a lot of pictures and paid a few hundred dollars in advance), or if I have not done so. it is a legitimate possibility that degrade the resolution images. A large number of fuzzy images have been digitized from the Disc format. They say that the small size and the presence of the central hub contribute to the blur. However, since then, I have discovered that even some of the 35mm format scans were fuzzy. All the blurry images are color negatives (I guess C41). I had B & W and color slides (positive) and even some 110 negatives that were great.