ive been thinkin of some great idea for my next dio, but does a dio have to be an event that has actually happened??

no !

actually if you don't want to make a dio based on an event :

for a german tank, you just put the balkenkruz and no number.
a lot of german tanks had nothing but the balkenkruz, at the end of the war
and even now the expert can't tell you wich regiment, panzer they come from
so...

I think it depends :

-you make your model for you and for you only, so you don't care, :-)
or
- you want to show it to others modelmakers, or show it in an contest
then maybe yes, you need accuracy and need to be "an event that has actually happened"
but beware, it's hard to do !
so do your best, and good luck !

No it doesn't. If you are trying to reproduce an event then yea. But if you have a few kits that would fall together in a cool diorama then No - it can be totally made up.

A lot of the time people share background surrounding the diorama to provide information about why a particular item is the it is. For example you wouldn't put a Tiger in day one of the Normandy invasion but if you want a Tiger on a cliff then say "somewhere in France before DDay". Does that make sence??

Of course the specific event does not HAVE to have happened. As long as the models hold together in a historical context. A king Tiger in the South Pacific or Marines on the Normandy beaches would be hard to justify. But a generic scene of a jeep passing a knocked out Panther certainly would be acceptable, even in the strictest of competition. It would be the judges' duty to prove that this never COULD have happened. And even then, if the basics of building are there and the story is internally consistent, it would be hard to disregard this in judging.

i'd agree,that as long as all your models are accurate and in the right context then go ahead!too many rivet counters exist all ready,and that takes the fun right out.Use books for reference AND inspiration,at least thats how i justify my trips to the bookstore

Diorama can be anything you want it to be. I would, if at all possible, try to stay within historic guidelines for your project but you could really have a lot of artistic freedom when creating a dio. IMHO the most important thing about making dioramas is to have fun.

When my son was young I had some figures from the tamyia 250 hannomag you know the ones running and climbing out of the vehicle.well I posed them on some rubble as if they were running in panic one climbing the wall, behind them i posed four of my sons star Wars Stormtroopers Tooled up and ready to rock,he got quite a kick out of it ,I dont think this event happened , but he enjoyed it so it was well woth doing #:-)

There is a lot of witten and pictorial history about modern campaigns. This does not mean that every single person was accounted for somewhere in a written or pictorial account. Keep your diorama faithful to period and location and let loose. As far as accuracy, that is up to you. Nobody knows everything. When reproducing history, we try to be as accurate as possible with the references we have available. I know little of the other judging formats, but the open system used at figure shows advises that the "judges" score the model building/painting skill, not the accuracy. A judge gives the builder the benefit of the doubt where accuracy is concerned.

That's pretty much the official IPMS policy as well. Storywise, however, it has to make sense. An egregiously incorrect story, where there were serious anacronisms, would have to lose points, regardless of the skill of hte builder. A diorama is judged on story as well as ability.

The best example of this would be the Korean or Manchurian who was captured on D-Day,what a vignette that would make! I can also imagine some of the rivet counters having apoplexy......worth doing in 120mm..only to see their faces....Jim

Or you can have a german Tiger battling a dinosoar with a town in the background (Probly would be a realy cool dio #:-)

Or luke Skywalker makeing strafing runs on German SS dug in trenches.

ANd think about the Sci-Fi, fantasy stuff (warrhammer40k) Those guys make huge dio's, and that stuff never happend.
Like Marty said, just have fun

Rivet counters have their place and are needed. It is because of them we have an "aftermarket". But since not every moment in time is recorded outside of memory then anything is possible. So as was said previously, Tigers on a cliff in Normandy at D-Day, no, that doesn't work. Tigers on a cliff, that works. If you are going to do a fantasy piece i.e. a Tiger painted with a camo scheme that looks like a tiger (orange, white with black tiger stripes. Works for tigers...) fighting a T-rex, then preface it with "fantasy piece" if you plan on entering it in a contest and you should have no problem. Its a fantasy, there is no precedence to judge it against. Technical maybe but not theme or time related. You're happy? That's all that matters. If the fantasy tiger is weathered or has claw marks on it then that is all the more interesting for you and the onlooker.

A diorama is a story or photograph, so long as that photo or story makes sense, and is well executed and aestheticly pleasing then no foul.

Look at Reign of Fire. Abrams Tanks fighting dragons. Would you not do a dio of that?