I am here to clarify some old stuff, pretty basic. Please correct me if I am wrong
Trailing is a current number on the numerator / a historical number in the denominator (Pt=1/Et=0)
Leading is a current number of the numertor and a current number in the denominator (Pt=1/Et=1)
Trailing is usually historical number in relation to a current value, if I’m not mistaken. Like ROE which is sometimes calculated as current NI over last year’s BV of equity (although the average is most commonly used). It’s still a trailing value because you measure historical performance.
However, I’m almost certain that leading indicators have to do with forecasts to current value. Like leading P/E ratios which use forecasted earnings over current price (the reciprocal of earning’s yield). Or leading EV/EBITDA ratios which use projected operating income before depreciation and amortization over firm value.