Since tractive effort is mostly based on weight (though modern wheel slip systems add more), it makes some sense that a switching loco is referred to by weight. The US military still seems to follow that example - a base I worked on a few years ago as a temp had "120 tons" (rebuilt GP9s), "100 ton" SW-8 and a "45 ton" rebuilt drop cab. Same concept for adding slugs were high TE is needed at slow speeds. There was a steel mill that even bought slugs to run with their industrial 45 tons.

If the GE builder's plate is still there - this is how to read them:

The first letters are the wheel arrangement - "B" means two axle, B-B means two-two axle trucks, B+B same but articulated, etc.

The next numbers are the total weight / weight on drivers times 1000 pounds. Unless the design has unpowered axles, the numbers will be the same. Powered can mean a traction motor; chain or siderod from an adjacent axle with a traction motor.

The next series are the number of traction motors; "GE", "GHM" or "HM"; and the model number of the traction motors. Note that GHM and HM are still GE motors, but from their (Gear) Hoist and Mining section.

For example:

B-B-90/80-2GE733 is a "standard" 45 ton
B-B-88/88-4GE733 is a standard 44 ton
B-B-90/90-4GE733 is a 45 ton drop cab (OERM #8580)
B-B-100/100-2GE763 is a 45 ton, ballasted to 50 tons, using the newer 763 motors
B-100/100-2GE741 would be a standard 50 ton for steel mill use, with heavier motors
B+B-100/100-2GE763 would be a "steel mill special" - a 45 ton ballasted to 50 tons on articulated trucks
B-B-140/140-4GE748 is a 70 ton
C+C-140/140-6GE747 articulated narrow gauge six-axle 70 tons for US Potash and export
B-B-130/130-4HM833 is a war era 65 ton
B-B-160/160-4HM829 is a war era 80 ton
B-B-130/130-4GE747 is a post war 65 ton - change to 160/160 for an 80 ton
B-B-100/100-4GE747 is the model of Southern Pacific narrow gauge #1

This is GE's official designation scheme. Be warned that GE often made variations that aren't always obvious. They also used the GE747 traction motor on 45 tons, B+B 47 tons and narrow gauge B-B 70 tons. The later 70 tons also got GE761 traction motors.

The builder's plate will also have the horsepower usually stamped on it, but this might be the gross hp or traction hp, or they might list both. On the later small U series and SL series, GE wasn't consistent about stamping those model designations. I've seen a SL series with the old industrial designation on the builders plates.

Even GE's "official" list of locomotives doesn't tell you that much - the owner, serial number, shipping date, weight, engine model, main generator and traction motor. It doesn't specify the cab type, wheel arrangement, gauge, horsepower, max. speed, or how many engines or traction motors.