My first instrument is trombone. I do know the feeling of this transposing mess. It is very similar to reading old music for trombone and suddenly tenor clef is in your face or even alto clef if your knowledge is being tested in an academic environment. It is all easy if you do it daily. But when this stuff comes at you only once in a rare while it can be embarrassing to say the least. On one occasion I can recall some prankster switching a sheet of music and I was playing counter melody in a quartet. As awful as it went never mattered. The audience knew nothing but I felt awful.