migrating from API 1 to 2 - how do I know if I have OAuth 1 tokens?

The old iOS Core SDK didn't have good documentation unfortunately. Here are the relevant methods/documentation in the comments though:

/* Loads the file contents at the given root/path and stores the result into destinationPath */
- (void)loadFile:(NSString *)path intoPath:(NSString *)destinationPath;

/* This will load a file as it existed at a given rev */
- (void)loadFile:(NSString *)path atRev:(NSString *)rev intoPath:(NSString *)destPath;

There wasn't a parameter for controlling overwriting at the destination.

The actual code is:

// Everything's OK, move temp file over to desired file
[fileManager removeItemAtPath:resultFilename error:nil];

BOOL success = [fileManager moveItemAtPath:tempFilename toPath:resultFilename error:&moveError];

So, yes, it seems it overwrote existing files by removing anything at the destination first, and then moving in the downloaded data (which it saved at a temporary location beforehand).