Each of those individual files is relatively small and may only be a single slice each. So this might be the slices for only a single volume. Note that there are other kinds of diffusion scans (or scalar output from the scanner such as ADC maps) which are not compatible with DTI analysis. You could share some (!anonymized!) headers to get feedback, see instructions here:
But probably the best option is to contact whoever is responsible for scanning these images to verify the scanning protocol.