Hi,

Maybe this in your first cell and drag down (not in groups of three, though; just this):

=IF(INDEX(INDEX(B:D;;IFERROR(1/(1/(MOD(ROWS($1:1);3)));3));3+ROUNDUP(ROWS($1:1)/3;0))>0;INDEX(A:A;3+ROUNDUP(ROWS($1:1)/3;0)))

Regards