I agree Joe, it's definitely a later sheath. It is possible that this Astro was ordered without a sheath and paired up with one later, as the only thing these Scaleless Astros were made for, was to display...as intended, for collectors. Bo even states so in the catalog, that there were Randall models more suitable for sporting purposes. It was at a time when the country was excited about going to the moon.
It's interesting that this one is from 1965, when Micarta was standard.