Quick links to individual issues by approximate date:
Special Issues - The "Introductory Issue" was first published in 1989 (approximately February, between Issues 45 and 46) and was intended to be mailed to all new RPGA Network members when they joined. However, not all new members received it and existing members generally did not receive it. This issue sometimes is called "Issue A". The "GenCon Issue" was published in August 1999 (between Issues 137 and 138).
Issues 1-148 and 161 carried "Volume" and "Number" indications either on the cover or in the masthead. However, after Issue 24 these often were incorrect (for example: both Issues 24 and 25 indicate they are "Volume 5 Number 3"; Issue 36 is "Volume 7 Number 3" and Issue 37 is "Volume 7 Number 6"; Issue 61 is "Volume 12 Issue 5" and Issue 62 is "Volume 11 Number 6"; etc.). Additionally, the printed month of publication is erroneous for Issues 87 and 124. The Issue number itself is always reliable. Issue 119 curiously has a printed cover price. Issues 129 and onward usually featured paid advertisements.
The magazine was not actually titled Polyhedron until Issue 5 (in 1-4 it was simply "TSR RPGA"). From July 1998 through April 2000, eight issues of a related but distinct magazine Polyhedron (Europe, Asia Pacific, Africa) were published in the United Kingdom, with Issues 5-8 also being published in Australia. Too, there are four issues of the related but distinct Polyhedron (German) published in Germany.
In January, 2002, Polyhedron was "merged" with Dungeon, both periodicals being published under a shared cover (often having two "front", but no "back" covers). Thus, Issues 149-171 are combined with Dungeon 90-113 (Dungeon 112 did not include a Polyhedron).
Issues 13-86, 101-143 were generally mailed with an outer "mailing cover" composed of a white paper cover stapled with the magazine and covering the actual cover. Per Jean Rabe (editor for Issues 38, 40-105) this was done to conform with changing US Postal Service mailing regulations (to obtain better mailing rates and services). The covers had content call-outs and game convention news but occasionally had cartoons, maps, or text pertaining to the issue's interior content (the earlier covers more so than later ones).
From March 2005 through November 2005, Wizards of the Coast distributed an occasional e-mail subscription that was titled "Polyhedron Newsletter", with each e-mail being numbered 171-181. These never were physically published and contained principally URL links back to Wizards' web site. Content was almost entirely product announcements and product reviews for various Dungeons and Dragons hardback books. Wizards did not archive these e-mails and today they are apparently wholly unavailable.