Recognising add-a-ball and novelty games
Add-a-ball games (introduced by Gottlieb in 1960 for areas such as Wisconsin and New York that banned free games) award extra balls instead of replays, and novelty games award nothing. Neither has a credit wheel, add-a-ball backglasses usually say 'balls to play', and a coin starts the game directly, often with no start button.
Systems
Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part Two, Clay Harrell (pinrepair.com)