When BIAB came out, there were only a handful of styles (the ones that start with ZZ, such as ZZJazz). Each of those had a number (and ultimately a letter) assigned to them. I don't have the Mac version, but on the PC version, if you select from the menu, "Styles, Choose from 24 Built-in Styles", you will see the number and letter assigned to the style. So Swing Jazz is #1, and so any song that used that style (which is ZZJAZZ), and would therefore have an MG1 extension.

Later, when there were more styles and user styles were made available, the file extension changed to final "U" extension (MGU). There is an option to either save everything with a "U" extension, or use the old convention for the original built-in styles.

So both songs are songs that have something on the Melody or Soloist track (versus those that don't, which are SGU or SG1 styles). They could very well be the same song; it just depends on whether the option to save with "U" extensions was turned on or not.

Hope that helped.

John

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