Shouldn't they have been, under that system, 452 (later 451) as they were 1980's designed units (not 1970s, as 44x classification suggests)?
The classification doesn't designate decade of build though.
The 41x series was essentially the first BR generation d.c. units (for Southern region), and included the EPB stock numbered in the SR series.
Then came the 42x series, which was second generation in effect.
The 43x series was used by the REPs, though the TC units weren't originally 438.
The 445/446 series went to the PEPs, though the 455s nearly became 510!
The 442s could have been 452, but as they used different traction packages, etc, to the 455s they were classified 442 (and with the PEPs withdrawn the 44x series was vacant).
The odd things comes with the Networkers. The 465/466 classification fits, but the long distance units for the Kent Coast were going to be 471 not 461 as logic would have suggested, given they were also a Networker.
444, 450, 458 and 460 have no logic at all in the numbering system! The only one that might fit is 444 - it was essentially putting the long distance, 23m body unit, in the same grouping (44x series) as the 442.