Win Mortimer took over as regular artist on the Legion of Super-Heroes in late 1968. Naturally, if you didn't take a good look, you'd assume he's the penciller of "Lament for a Legionnaire" in Action 384 (Jan/70). Well, he may have touched up the figure of Element Lad in the splash panel. But otherwise Curt Swan returns for his final bow on the strip's first run.
If it explains the long-standing misattribution, Swan is being
inked on this story by Jack Abel, the regular on the strip at this point, whereas on the very same issue's Superman
story George Roussos is his inker.
Nelson Bridwell mistook Swan's 1952 art for Mortimer's in the reprint
of the Batman story "The Masterminds of Crime." He was corrected and
ran the correction soon after.
But certainly by 1970 (if not as early as 1952), Mortimer's and Swan's art styles don't look very much
alike, do they?