The difference between biographies and autobiographies
Whenever possible, I use both biographies and autobiographies when doing profiling. Their functions in the process are radically different. Biographies, ideally, contain facts. Mostly what you need to write a decent one is an interest, a lot of bloody-minded persistence, and a basic knowledge of stuff like municipal records and skip tracing. I find them very good at providing context, and almost useless for trying to crawl into someone else's head. I have seen some excellent ones that were written for very personal reasons, such as Andrew Hodges' biography of Alan Turing, but by and large the point of a biography is to gather things that are known and hard records of things that both the subject and other people said, not to editorialize. They are merely boxes in which the puzzle pieces are conveniently collected.
It should go without saying that I don't consider myself a very good biographer, particularly not when I'm doing this. I only do these things when I trip over someone that I for some reason find fascinating, and I'm heavily biased towards investigating the parts of their work or history that set off some flag or another in the back of my brain. What my audience sees is not an impartial picture of someone who did a thing I like, it's a recounting of an impression of my experience of investigating them. These things are not photographs; they are interpretive paintings.
Autobiographies, by contrast, are exceedingly helpful. Their value lies not in recreating timelines or gathering documentation, but in laying out for me what things the author found important enough to recount, and why. A lot of Chaplin's scholarly biographers get very snippy over the fact that he plays fast and loose with details sometimes, and omits entirely things he just doesn't feel like going into. (Sometimes he acknowledges it, sometimes he doesn't. He flat out says he's not going to talk about Lita Grey at all, on the grounds that he loves his eldest two children very much and would like to remain on speaking terms with them.) I don't particularly care. This isn't investigative reporting here; this is someone telling stories over the dinner table. It's watching what stories they choose to tell, listening carefully to how they tell it, and noting what they think the point of that story is, that sheds light on things for me.
As a rule, I take any actual fact presented cum grano salis, especially if time, distance or death have made it impossible to corroborate, and assume that the dramatic perfection of actual events is at least 50% lower than the anecdotes make them sound. I don't assume anyone is making shit up wholesale unless one of my internal detectors goes off; being that pathological about it is likely to stir up much larger arguments than the endeavor is really worth, and anyone who insists on playing Baron von Munchhausen despite that is generally crazy enough to also set off a lot of the other emergency fweepers.
What I do assume they are telling the truth about is how they feel. As House says, everybody lies, and everyone has their own reasons for doing it. If nothing else, memory is notoriously unreliable and melts into confabulation over the years. An equal truism is that it is vanishingly rare when someone changes their accounting of their feelings in order to fit how they remember the facts -- people instead change the facts they recount in order to match the feelings they remember. If someone recounts a tale about meeting John Q Randomguy and immediately taking a dislike to him because Randomguy was mean to the local dogs, then whether this specific meeting happened at the time and place given, and whether Randomguy specifically kicked a dog during it, is something you'd have to take up with the other witnesses, if there were any. But it does tell you, with a pretty good rate of both specificity and sensitivity, that dog-kicking is something that does not go over very well with the autobiographer. And also that he probably genuinely, for whatever reason, doesn't like John Q Randomguy.
With many performers of the era, the question of "autobiographies" is complicated by the fact that studios considered the public faces of their contracted actors to be a creative effort equal to or surpassing those that went onto film. There is at least one "autobiography" of Chaplin that predates My Autobiography by a good fifty years. As noted in the editor's introduction, it contains a lot of information that could only have come from an interview with Chaplin, but the tone and voice are so extraordinarily different that I am comfortable, despite the time difference, in concluding that the two books were written by two entirely separate people. The earlier is far more likely to have been written by a studio-employed random who might, if it happened to occur to them, have remembered to forward a copy to Chaplin when it was published. If either is entirely genuine, I would bet on the latter.
The impression that I get of Chaplin is that the anecdotes may or may not be consistent with the factual record, but the personality in the book is consistent with the personality on film, and the personality responsible for the screenwriting behind them. I think the notorious fluidity of some of his stories is summed up rather well by one of the illustrations in his last book. There are pages of photos interspersed with the text, and on one of them he has chosen to reproduce a painting he did of his wife Oona when he was trying his hand at watercolors. There doesn't seem to be any particular reason for this; neither that painting nor the watercolors are mentioned in the text. There are other photos of Oona (née O'Neill), and she is a trim, pretty lady, alert and dignified, with a pale face defined by jet hair and jet eyebrows and a slash of fashionably dark lipstick. But in Chaplin's painting, her profile is breathtakingly poetic and beautiful -- recognizably Oona, but with the studied imperfection of art.
I would not be surprised if this were the way he treated his entire life. It does make things difficult for other people sometimes, particularly people who are in charge of practical matters like money and studio equipment. But it also means that a lot of people who have to deal with you come away feeling special somehow, as if you'd plucked them out of a crowd for a role in your own personal art project. Whether this also makes them want to wring your neck depends on whether you're writing yourself into a witty comedy or a lurid soap opera. Chaplin was not exactly an unmitigated ray of sunshine, but whether unconsciously or through artifice, his laughter was far more contagious than his gloom.