MIke D explained it best
in layman's terms transcription is writing what you hear as close to the original, an arrangement is composing a piece based on existing work, with variation in music and/or instrumentation... simply writing note for note in another key is considered an "arrangement".
one more time, from an actual professional:
TRANSCRIPTION AND ARRANGEMENT AREN'T THE SAME THING, REGARDLESS OF THEIR NOUN OR VERB FORM.
and no, it wasnt 1994 Blue Devils that "it all began"... you can go further back than that to see intricate variations on a theme, etc.
Look at 82 SCV... or 79 Spirit of Atlanta.... 84 Cadets (aka Garfield)... 1983 Blues in the Night, Spirit is a good example... the entire 1985 Star of Indiana Show, 86 Suncoast....or how about 1988 Suncoast, although original music from Robert W Smith, it pays homage to recognizable music throughout... technically 89 Suncoast... although the arranger is the original composer, 89 is based upon the 85 work...
Crown's first year... with The Music Man, absolutely nothing like the original, if anything an improvement over the original
1991 Blue devils
1992 Star
1993 Blue Knights
tasty and interesting music being carved out of existing pieces is nothing new...