Hi there,
some days ago I ripped the music from the "Earthworm Jim 1 Windoes 95 Edition" CD with Exact Audio Copy. There the soundtrack contains 16 files, the soundtrack you get when you buy the games on GoG only has 14 files for Earthworm Jim 1.
I've made a chart to show which songs are missing and to show the differences in the song naming, because the ones from EWJ Win 95 have other titles sometimes and most of the songs are shorter.
Here's the chart (I'll also add a picture of the txt file to the attachments).
Earthworm Jim 1 Earthworm Jim Special Edition
-Tommy Tallarico - 01 - Banjo Race -Shiny Entertainment - 06 - Andy Asteroids
-Tommy Tallarico - 02 - Snot A Problem -Shiny Entertainment - 10 - Snot a Problem
-Tommy Tallarico - 03 - Party Time (longer with moderator) -Shiny Entertainment - 13 - Continue
-Tommy Tallarico - 04 - Falling -Shiny Entertainment - 12 - Buttville ~ The Descent
-Tommy Tallarico - 05 - What The Heck (The Oneups Remix) -Shiny Entertainment - 15 - What the Heck
-Tommy Tallarico - 06 - Buttsville -Shiny Entertainment - 11 - Buttville ~ The Queen's Lair
-Tommy Tallarico - 07 - Bass Mix -Shiny Entertainment - 17 - Start
-Tommy Tallarico - 08 - Junk It -Shiny Entertainment - 18 - New Junk City
-Tommy Tallarico - 09 - Bo's Annelid -Shiny Entertainment - 19 - For Pete's Sake
-Tommy Tallarico - 10 - Psycrow -Shiny Entertainment - 20 - Psycrow
-Tommy Tallarico - 11 - Darkworm Rag -Shiny Entertainment - 21 - Who Turned Out The Lights
-Tommy Tallarico - 12 - Submerged -Shiny Entertainment - 22 - Level 5
-Tommy Tallarico - 13 - You're The Best! -Shiny Entertainment - 27 - Difficult Ending
-Tommy Tallarico - 14 - End Theme (same as Party Time, shorter) -Shiny Entertainment - 13 - Continue
-Shiny Entertainment - 23 - Practice Ending
-Shiny Entertainment - 09 - Big Bruty

Still no answer? =/

The level Big Bruty isn't in the version of the game GOG has. It was in the Win95 Special Edition. Also it had a "practice" difficulty I guess, which gave you a lame ending where instead of talking about how you're the best they explain what the word worm means.

In the downloadable soundtrack on GOG.com. Party Time (The third track) has a different version of "What Are Worms?" after it plays the ending song.