JW (then president of the Swiss mission) explicitly teaches belief in HM in a poem.
Jabez Woodard, "Our Existence—Past, Present, and Future," The Mormon 3 no. 24 (1 August 1857): 1
Oh, we've been, yes, we've been in a bright world before,
Where we liv'd with our Father and Mother of yore;
And they nurs'd us as those that were tender and fair,
And wreath'd with fresh flow'rets our beautiful hair.
. . .
So our garments are chang'd and our glory hath fled,
And the sackcloth is ours and dust on our head;
And our Father and Mother are hidden on high,
And the storm-clouds are black in the wint'ry sky.