The first oops is a mechanical oops (including forgetting something about a character’s mechanical attributes).

The second kind of oops is Martin’s examples above, setting or story oopses.

The two kinds of oopses bear somewhat different consideration, but overall, I think the biggest point to consider is if retconning will take success away from the players. In the case of a mechanical oops, if it’s discovered immediately, it may be ok to take success away from the players so long as doing so is just correcting a mechanical error, and not making player’s choices irrelevant.

In the above examples, it’s pretty clear the only one that might be reasonable to retcon is the building. And then it’s a simple case of looking at what is changed by changing the building? Does your adding a story to the building change the decisions the players would have made? Did they decide not to put scramblers on the roof of their HQ because the neighboring building wasn’t taller than theirs? Did they then spend the money they might have used for the scrambling device for something that isn’t trivial to retcon? It’s also worth asking why does it matter? If it’s because you have a scenario all written up for the building and maps drawn, must that scenario happen in that building?

In the last two examples, the problem is the players were given information they should not have normally gotten. It’s really hard to take back information. And changing the value of the information after the fact is very dangerous. Doing so may make player decisions irrelevant. Of course if the meaning of the information is emergent and not predetermined, then there really isn’t a problem. For example, in Dogs in the Vinyard, the GM has a very small amount of predetermined information, everything else that the GM presents in play is emergent. The interpretation and judging of that information is up to the players, so who cares if you had written one thing in the town description, and accidentally said something else? The only problem is if you screw up the information so badly you break the chain of sin, but even then, really the worst that can happen is the situation isn’t quite as explosive as you thought, but that could happen just because one of your bangs misfires because it didn’t interest the players. In such a case, just toss a new stick of dynamite on the fire.

Frank

on the flip side, i don’t always have all the blanks filled in when i create an NPC or situation, and i’m free to further develop things later as long as it doesn’t conflict with established facts.

1. I don’t have enough facts to comment on why the building is problematic. If it’s too small, add sublevels or a skyway/subway to another building. If it’s too large, part of the building is unoccupied (construction is still going on or part of the building “fronts” as something else).

2. I wouldn’t retcon the secret. In this case preventive measures should be in place. This sounds like a D&D scenario (magic is involved) and I always build trapdoors in case important NPCs are killed. If the secret became problematic, I’d move the NPC offstage and open a trapdoor.

3. This one is the most fun. Yes, the Don always sweeps his apartment, but does he do it himself? Who sabotaged the equipment? Is someone else recording conversations? Maybe the Don himself recorded the conversation in order to have leverage later, so he faked his sweep.

Walt