FLAC encoders – any difference in output between the command-line tools?

I would like to know if there is any difference in the final output between the various command-line tools for encoding FLAC files, like ffmpeg, sox, the “official” flac etc. In some contexts, I have noticed that it's recommended to use flac over the others, but given that FLAC represents lossless encoding, am I correct in assuming that they should all produce identical output (given the same options)?