How creditable is the pop-info on MP3 encoder?

[MadiZone]

Hello.

It seems like your popup info on mp3-files is very radical when it have to decide which encoder has been used for the files.
Some files are displayed with the same encoder all the time, while others can change between FastEnc, Xing and QDesign rapidly....

How do I know for sure when it speaks the truth?

[Spoon]

For the Lame ones it is very accurate as in the mp3 files lame writes 'Lame x.xx', for the rest it just guesses.