12.4-5 and -6 are basically combining 12.4-4 and the load combos in 12.4.2.3. They're just explaining there that when you use 1.2D, you should add Ev, and when you use 0.9D you should subtract Ev. The idea is that you are "worsening" the effects of DL with the vertical EQ load. So if DL is...
Yes, this is a mistake in the SEAOC Blue Book. I caught it myself when studying this fall, and have verified with one of the editors that it was an error and has been corrected in the latest versions. They make that same mistake in at least one other problem. The +/- is the issue. You want...