This issue is a variant of Superman (DC, 1987 series) #19 [Direct]. There exist further variants.
This variant has "3RD PRINTING" listed at the bottom of the indicia. Apparently it came out much later than the first printing, with house ads in it copyrighted 1989 (and advertising issues 41 and 42 of this title), and a subscription ad that expires on "5/31/90".
All of the House Advertisements and Ads are different in this printing than in the first printing. And the letter column is only one page instead of two, truncating in the middle of a letter.
Story continues in Adventures of Superman (DC, 1987 series) #442.
Letters from readers - Brian Simpson, Jeff Mitchell, Roger D. Case, Joe Frank, Mathew A. Young, Ann C.H. Brachwitz, Dennis Tucker, Stephen Robinson, Jonathan Ezor and Greg Manter - and responses from Renee Witterstaetter.
The third printing only has the first of the two pages, stopping in the middle of Ann C.H. Brachwitz's letter.