From 1987 to 1988, Quality Comics published two versions of each issue, a U.S. edition and a U.K. edition. The covers and contents were sometimes different (these differences are noted in the individual issue bios). Most of the editions can be identified by a notation made in small type at the top of the spine of the first or last page.
Quality Comics eventually got the issue count back in sync, via the dual numbered U.S. editions and going forward published only one edition of each issue.
U.S. editions of Sam Slade Robo Hunter were published for #1-33 with two dual numbered issues (21/22 & 23/24). The U.K. editions ran from #8-24.