From the introduction:
X1: The Isle of Dread has quite an interesting publication history. It was the first adventure to feature a wilderness setting, and to include numerous new monsters. It includes four different printings, with the first three being fairly similar, and the fourth edition having significant changes to formatting, art, and even some content. This essay is based on information gleaned from The Acaeum, and the author encourages the reader to seek out that reference for more information of the publication history of this module.
Published by TSR in 1980, the first printing featured a dark blue cover and cover art by Jeff Dee, an old-school artist of renown with many classic D&D illustrations to his credit. The cover art features two adventurers on a small boat observing a pair of tribesmen attacking a dinosaur or dragon-like creature on a beach. On the top left corner is an orange diagonal stripe that says, "For Dungeons & Dragons® Expert Set". The back cover featured a color illustration by Bill Willingham depicting three adventurers battling a serpentine form in thigh-deep water. The first printing of X1 was the first color module produced by TSR, as previous modules were monochrome. This printing was included in the first printing of the D&D Expert Boxed Set, but it was also available for sale separately. Inclusion in these boxed sets in addition to being available for individual sale make X1 one of the most widely distributed on the classic TSR adventure modules. Although the module cover is labeled copyright 1980 (which is correct), the module booklet is labeled copyright 1981. There were also some issues with the product code being mislabeled in this printing. Some copies have the erroneous product code 9034 (which is actually the product code for B2: The Keep on the Borderland) instead of the correct product code, 9043. In addition, the last line of text on the cover is repeated: "All Rights Reserved".
The second printing occurred in 1981, and largely was the same as the first printing. One notable difference is a common lighter shade of blue for the cover, although it is unclear if this was done on purpose, or merely variations in print colors. This printing was included in the second print run of the D&D Expert Boxed Set, and it was also available for sale separately. Although the repeated "All Rights Reserved" text on the cover was removed on this print run, the product code discrepancy with the first printing is still occasionally present.
The third printing is virtually the same as the second printing. This printing was packaged with the third printing of the D&D Expert Boxed Set, and, too, was available for sale as an individual module.
The fourth printing (1983) of X1: The Isle of Dread is very different to previous printings, and similar to other modules produced by TSR in the mid-1980s. It features an orange-red cover, with artwork by Tim Truman. This artwork depicts a band of three adventurers standing in rocky water, battling a Tyrannosaurus rex, with a small sailing ship stranded on the rocks nearby. The diagonal stripe is gone, replaced by a dark blue horizontal bar labeled "Xl" and the (correct) product code. The updated "block letter" TSR logo is prominently displayed on the front cover and the title page. Although the back cover lacks artwork, there is now a text teaser of the module plot and a contents summary. This module was edited by Tim Kiplin, as credited on the title page which now includes a preface.
Notable changes to the interior include a new font type and format. The second page is a detailed table of contents and list of tables and maps. A sidebar listing all abbreviations used in the stat boxes is now located on page 3. All of the artwork has been replaced with updated pieces, including for all the new monsters described in the appendix. These occur on the upper border of the last two pages of the booklet. See pages 3, 5, 6, 11, and 28 (not particularly well spaced throughout the book, mind you) for the new artwork. Rory's diary (a Player's Handout) has been reprinted as a sidebar with an old parchment background on page 5. In addition, this handout is reproduced as a dual color part of the gate-fold cover, with the opposite side featuring a full color Player's Handout of Rory's sketch of the outer parts of the isle. All maps have been renumbered, and there is an obvious omission on Map 12 (Temple Level 1). In the first three printings, near area 5 (renumbered area 34), there was a sketch displaying the route from area 3 (now area 32) passing under a raised platform in area 5 (now area 34) to the corridor leading to the lower temple levels. This sketch has been removed in this printing, so now it appears there is no access to the rest of the dungeon. There is a letter "N." now on the map, which is a reference to the room description.
Further, several of the encounters were altered with different monsters, apparently to bring this printing in line with monster statistics available in the Basic and Expert Sets. For example, in area 2, the five bull sharks were replaced with four crocodiles. Area 6 was formerly the lair of an ancient giant squid, but in the fourth printing this has been replaced with a water termite. Area 24 once featured a sea dragon, but was replaced with a sea hydra (depicted in artwork on page 6) instead. In the lower level of the temple, giant crabs replaced the three albino mako sharks in the Chamber of the Great One, and more crocodiles replaced giant piranhas in a nearby corridor. It always vexed the author how open-water sharks could survive in a small underground chamber with freshwater fish lairing nearby. Thus, these latter two changes actually make some ecological sense, although logical dungeon ecology in the early 1980s was mildly (at best) observed.