By the leading '6' in the pattern number (62009 1/2), the original would've had to be in bone (smooth or jigged) or any other jigged handle material, like jigged synthetic/Delrin or jigged wood (Case's 'Staminawood'). That would be according to Case's own handle material designations in pattern #s beginning with the digit '6'.
So, originally, I'd bet it was either bone or jigged Delrin.
Case's own designations would specify a leading '8' in the pattern # for 'Genuine Mother of Pearl' or a '9' for 'Imitation Pearl'.
A note in a collecting guide I refer to, mentions that Case stopped using genuine mother of pearl in 1975, excepting one pattern (82079 1/2). Your knife was manufactured in 1979, indicated from the 'one dot' tang stamp shown. In more recent years, Case has occasionally had limited runs in Mother-of-Pearl, with those knives following the pattern# convention, beginning with '8'.