barelystayingsane on "Equivalent Units Question for People Using Becker 2013"

At the top of page B1-51 in the Quantities section under the Conversion columns, why are "Units in process, May 31" stated in equivalent units but "Units in process, May 1" are not?

For consistent treatment, wouldn't it be either

Treating both as equivalent units:
Units in process, May 1 - 1,600 (4,000 x 40% complete)
Units transferred in - 14,000 (10,000 + 4,000 x 60% + 2,000 x 80%)
Units transferred out - 14,000
Units in process, May 31 - 1,600 (2,000 x 80% complete)

or

Treating neither as equivalent units:
Units in process, May 1 - 4,000
Units transferred in - 12,000
Units transferred out - 14,000
Units in process, May 31 - 2,000

Thanks!