Anniversaries are important to comics. So important, in fact, that we make up anniversaries in order to celebrate them.
Case in point: when I started up a subscription to Amazing Spider-Man, the second issue I received was #365, Spider-Man's 30th Anniversary issue. It had been 30 years, to the month, since his debut in Amazing Fantasy #15. The event was commemorated with an extra-sized issue (which made me promptly fall in love with Mark Bagley and the Lizard) that had a holographic cover, re-enacting the cover scene from Amazing Fantasy #15 in stunning rainbow-colored 3-D.
Ten issues later, the book celebrated another anniversary of sorts: the #375th issue. It was doubly special, because it also marked the 30th Anniversary, to the month, of the publication of Amazing Spider-Man #1, the first issue of Spider-Man's first ongoing series. Venom guest-starred, Peter's parents "returned," and the event was commemorated with a shiny semi-holographic cover of some sort.
This is not all that uncommon. Comic books like to celebrate. #1 issues are, naturally, big deals. Any issue that ends in More than one zero is, as well, cause for celebration. Major year dates (any character's XXth anniversary, naturally) and issue number multiples of #25 are nearly always significant. ASM had only fifteen issues prior to that 30th Anniversary bash released #350, an extra-sized issue in which Erik Larsen departed as artist, and a bunch of people did pin-ups in the back. Also, I believe Dr. Doom was involved, and Uncle Ben showed up as a concussion-induced hallucination of Peter's.
In other words, #375 being the anniversary of ASM #1 wouldn't have mattered, they would have celebrated anyway. It just gave them the excuse to use a holographic cover twice in the same year.
These days, it's so difficult for a comic to gain a foothold that even 10th, 12th, 20th, and 24th issues are being celebrated. Part of this, naturally, comes from the "writing for the trade" trend, which would suggest that issue #10 or #12 is probably the end of a major story arc. There's a certain sadness in this, but it has led, at least in part, to the end of the holo-cover-every-week syndrome that plagued the '90s. And, of course, one could make the case that celebratory issues have greater meaning now, since most comics today don't make those impressive double-zero milestones.
Of course, if they'd stop ending and restarting long-running series, that problem wouldn't be so significant. After all, are Amazing Spider-Man or Fantastic Four selling any less now that they've returned to their original numbering schemes? I'd be willing to bet that the 500th issue extravaganzas of those series would have far outsold another #33 or something. The last few weeks have seen the final issue of The Flash and the death throes of Wonder Woman and JLA, the former two series well into the 200-issue range. We know that both of them are receiving relaunches in the near future, as is JLA, which has around 125 issues under its belt. Superman is being cancelled, only to (according to rumor) be replaced with Superman: Confidential, another #1 to add to the pile.
I started my Superman subscriptions (yep, I still receive Superman comics via mail) in 1992. Since then, I've seen one new quarterly series (Superman: The Man of Tomorrow), two new Maxi-Series (Superman: Metropolis and Superman: Birthcrap), countless mini-series and one-shots (Hunter/Prey, Doomsday Wars, Day of Doom, Superman Red/Superman Blue, Superman Forever, Superman: Legacy, Save the Planet, etc.), one new (semi-)regular ongoing series (Superman/Batman), and now the cancellation of two regular series (Superman: The Man of Steel and Superman). I know the subscribers make up a pretty small chunk of comics buyers, but does DC realize how much it screws up the math to try to split up the remaining issues of one series among the other three? Sigh, it's a pain in the butt. I think, once my subscriptions finally run out, I have at least one extra issue of Action coming. Of course, the cancellation of Superman might even that problem out, if "Superman: Confidential" doesn't take its place in my mailbox.
Anyway, the point is that there's the perception that #1 issues sell better than higher issues; that large numbers intimidate people. Poppycock, I say. Honestly, did the high numbers prevent people from picking up "Hush"? I say thee nay.
Of course, not every comic can have Jeph Loeb and Jim Lee working on it (thank goodness for small miracles) to boost sales. I can't speak to the factual truth of that perception, so I'll let it go, but I sure like seeing #500 more than #1. Everyone gets a #1.
I own a bunch of these anniversary issues, from various series. Like I said, there's one every 25 issues almost guaranteed. Typically those issues contain major changes that are eventually undone, or are the culmination of major storylines, which usually restore some sort of status quo. Off the top of my head...
Action Comics #600: Superman and Wonder Woman kiss, ending any chance of their eventual relationship up until Kingdom Come.
Superman #75: Killed Superman. He got better. Came in a black polybag with all sorts of goodies.
Adventures of Superman #500: Superman and Pa Kent meet in the afterlife during Pa's near-death experience. Also introduced the four wannabe Supermen. Came in a black polybag, the cover had some sort of inexplicable plastic clingy thingy.
Superman #82 and Adventures of Superman #505: Not anniversaries, but respectively contained the end of the Reign of the Supermen storyline and the restoration of Superman's costume and status quo. The former had a chromium cover, the latter a holo-foil one. All hot on the heels of that polybagged AoS issue. If that's not a little excessive, I don't know what is.
Superman #100: Kicked off the "Death of Clark Kent" story, where Superman gave up his civilian identity due to the machinations of the Green Go--er, Conduit, a villain who was really kind of wasted.
Action Comics #700: somewhere in the "Fall of Metropolis" storyline. Metropolis fell down. It got rebuilt. Repeatedly.
Superman #200: Mercifully ended Stephen Seagle's reign of terror on the title, killed Cir-El, caused the greatest sigh of relief ever breathed by Superman fans, right up until Chuck Austen left the book.
Superman: The Man of Steel #100: Introduced Superman's second post-Crisis Fortress of Solitude; started a tradition of Mark Schultz being the only writer to understand that Fortress.
Wonder Woman #100: Killed Artemis, restored Diana as Wonder Woman, got her to give up the half-jacket and bicycle shorts.
Flash #100: Killed the Flash, introduced the Speed Force (which lasted what, 125 issues? That's quite the status quo alteration).
Flash #200: Brought Wally's kids back, answered the question of the new Capt. Boomerang's parentage.
So, what are your favorite anniversary issues? What changes managed to stick around? What was undone within a year?