It is not just the Bible Stories book depicting only one nail being used in Jesus' hands. As far as I recall, all of the WT's depictions of Jesus being named to a stake (of the kind lacking a cross beam to support the body) show only one nail driven through the hands. Many of the illustrations show a slanted board under the feet (with one only nail going through the feet) providing some degree of support to the body - and thus eliminating the need for more than one nail being needed in the hands for support of the body.
I'm not aware of the WT ever saying (at least during the years I was an active JW) that multiple nails through the hands were needed to support the body weight of Jesus. When I talked to a JW elder about the reference to nails in Gospel accredited to John, the elder told me it says "nails" because a nail was also used for the feet in addition to a nail for being used for the hands. But I didn't accept his explanation since the verse doesn't say "in his hands and feet the print of the nails" but instead says "in his hands the print of the nails". Note that John 20:25 (1984 NWt) says "... Unless I see in his hands the print of the nails and stick my finger into the print of the nails and stick my hand into his side ...". That verse says nothing about the feet and thus nothing about the print of nails (or a nail) in the feet.