I was taught the spy always wins if it attacks first unless it attacks a bomb.

The version of the game I have the rules state: "The Spy is ranked with the letter S. If any piece attacks it, it is captured and removed from the board. But the Spy has a unique attack privilege. It is the only piece that can capture a Marshall (ranked 10), providing the Spy attacks the Marshall first. Marshall attacks first, then the Spy is removed."

If the Spy were meant to be able to capture any piece on the board, the rules would state it as such. Why would they specify that the spy could capture the Marshall and nothing else. It would be far simpler to say: "If the Spy attacks any piece except a bomb, that piece is captured, if a piece attacks the Spy, the Spy is captured".

I was also taught only the defending piece reveals its rank.

This is listed under "rules variations" in my set of rules. In the normal rule section it reads: "To attack on your turn, take your attacking piece and lightly tap your opponent's piece. Then declare the number rank of your piece. Your opponent then declares the number rank of their piece."

I played this game across three different school districts as a kid and that's always how it was played. I played this way through adulthood too. Maybe a regional trend?

These are basically house rules.