Rather than debate the merits of ret-conning, let's go for a case study. What's your most memorable bit of retroactive continuity, good or bad? What, if anything, would you have done differently?
Retcon isn't a big feature of my games--but when it needs to happen, I'm of the "make it seamless" faction rather than the "re-write the stuff we don't like" faction.
Which means to me, Han shot first, not Greedo, no matter what the DVD says. I think that you should be very very cautious in erasing "errors in judgment". Once the past tapestry is that squeaky clean, we lose our faith in present credibility.
My own pick for most memorable is from the play of Empire of the Gleaming Banner.
In the backstory conceived by the Players, Prince Gerard had made a visit to the realm and was directly related to one PC. This amounted to treason by the Lady Canthraal. This didn't quite suit my idea of keeping Darrheabarr as a different canvas that could have cameo visits by canon characters--but it was so early in the process that I just flagged this with "PC believes Gerard is parent".
When I flag stuff like that, I know it isn't likely to stay the way it is writ.
Further inspiration arrived when another PC explained later that she had had an affair with an Amber royal. I assigned this fact to March, son of Gerard. If Gerard was making visits to Darrheabarr, then his son would be a likely person to visit as well.
After a very small bit of data exchanges and further questions about the realm from Players, it clicked with me that these two events were not separate. And connecting them also packaged up the notion that Canthraal had not been open about her relationship with Gerard.
The RetCon was:
Canthraal had mistaken a large strapping royal from Amber for Gerard at a event in shadow. She had initiated a mental dominance of this fellow in order to get him in bed, because she had very secret information that Darrheabarr's stability and reality was waning. With Lora's aging, the long absence of Delwin, and the death of Sandmorel's children, the Empire was losing the favored status of having intimate ties with Amber's own stable influence on shadow.
Canthraal believed that having a child of Amber would work to shore up that stability and draw Amber's attention back to Darrheabarr. And if she got thrown in prison for that, well, that was the price.
It worked, and along comes Jubilation. (Get the name tie-in?) Father is March, not Gerard.
But much later, though Canthraal has forced March to forget about the event, March is drawn back to Darrheabarr. He explores. He thinks the place is familiar. He has a fondness for the people. He meets 2nd PC female.
They have a very brief and very hot affair.
That affair breaks the block in March's memories. He realizes he's been had and walks out without blaming 2nd PC at all. (Or explaining things.) He does go confront Canthraal. Shamed but desperate, she actually gets the better of him again and erases the event a second time.
She sends March away.
This results again some years later in March discovering Darrheabarr and finding the place haunts him for some reason. He explores. He tries to work out the deja vu of walking the sunwashed streets.
This time he is captured by citizens because he slips and allows them to see a unicorn emblem on his effects. The folk of Amber must have specific permissions to enter the Empire. When captured, the officers mistake him for Gerard, and thinking that he'll get better treatment, March keeps his mouth shut about who he really is.
And towards the three-quarter point of the game during the run, the PCs hear that Gerard has been captured spying on the city.
Bringing the whole thing around in time for everyone to get very excited and juice up the drama of the end movements of the game.
The PCs dealing with the 'big man' behind the bars assumed it was Gerard, which reinforced the expectations of several PCs running around who hadn't even gotten to talking to the prisoner.
And when the endgame hit, who March really was played out as a significant stress on Canthraal, Jubilee, and much of the family.
And another sort of RetCon slant over at 20x20 Room.
This may be our last Lunchtime Poll, but thanks for the meme.