D51-498 was this loco special?

I know exactly what you mean, but having looked into it everything makes sense (typically japanese)

Briefly D51-498 breaks down as;

D = 4 Driving Wheels (E = 6 Driving Wheels, C = 3 Driving Wheels, B = 2 Driving Wheels)
51 = Class number (10-49 = Tank Locomotive, 50-99 Tender Locomotive)
498 = Serial number of the individual locomotive (i.e. 498th built)

I suspect the reason for the apparently different D51-498 pictures around simply reflect different era's of its life after various re-builds. Having read more it was initially restored in 1988, the more recently in 2009 after a major failure of some sort.

Apparently

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More info here on the designation numbers etc... and the D51-498 specifically;

Joyfull Trains