This data set provides information to uniquely identify an spectroscopic observation. The data is here.
The files includes the following columns:

zero-indexed position in the data of the NYU VAGC DR7
[Note] The full set of spectra is in sdss_spectro_catalog.fits in the NYU-VAGC DR7
Plate Number
Plate number of observation
MJD of observation
fiber ID
fiber ID (1-640)
zero-indexed position in the data of the MPA-JHU DR7 spectral measurements; -1 if not matched.

Caveat: for column (2) to (4),  -1 for galaxies with redshift borrowed from the nearest neighbor and -2 for ones with redshift taken from other than SDSS. If you want to study the galaxy properties, ignore galaxies with negative bits for column (2) to (4).

The data of 114,303 galaxies with rP > 17.6 are also available here.