The black label design is the first, as that shows (C) 1972 at the label circumference at the bottom, whereas the rainbow design shows (C) 1973; copyright years shown on the various MCA label designs are copyrights for the designs.
One of them; they definitely had different catalogue series for various prices and configurations. Neil Diamond's Hot August Night was MCA2-8000, thus the first in that series of two-record sets in a certain price. This would have been the first in the MCA-2100 series; the first in the MCA-300 series (presumably $1.00 lower than MCA-2100's) was Entertainer Of The Year by Loretta Lynn (MCA-300, natch'), while MCA2-10000 was a repackaging of the Jesus Christ Superstar double album (originally Decca DXSA 7206). Presumably, January-February 1973 was when the "black rainbow" label was first introduced, thus plain black labels of both LP and 45 would have been first.
Added inner gatefold images, 12 page booklet and Capitol Record Club labels (which aside from the catalogue number change on the labels, the cover and booklet are the same as the standard issue with no number changes/additions)...John