Agree with this. Claiming a Tag on a GGG or GWG is an exploration goal of mine. But with only four of each known in the Galaxy so far, the odds are very, very low.
Every star has a "Goldilocks zone", the area within which it is not too hot, not too cold, and an Earth-like planet can theoretically exist. The current atmospheric composition, surface temperature and presence/absence of water is irrelevant. Any planet orbiting within the Goldilocks zone is likely to be a terraforming candidate, so long as it is (a) not too heavy - surface gravity below 4 G; (b) not too light - surface gravity above 0.08 G; and (c) orbit not eccentric i.e. so elliptical that the planet regularly swings in and out of the Goldilocks Zone.
When scanning planets in the Goldilocks zone, don't ignore the moons. Moons in the Goldilocks zone are always Rocky, but if they're above 0.08 G, they are likely to be terraformable too.
After exploring for a while, you tend to get a feel for roughly where the Goldilocks zones are for the different star types. But look at Sol as an excellent example: Sol is a typical G-class star and Earth is 500 Ls away from Sol and right in the middle of Sol's Goldilocks zone; so for G-class stars, 400 to 800 Ls is a good typical range to hunt for terraformables. For smaller, dimmer stars (eg K class) the zone is closer, for hotter, brighter stars, it's further away.
Multiple-star systems tend to throw off these calculations, as the stellar forge considers the heat supplied by each star to be additive. But as a general rule, multiple stars tend to make the Goldilocks zones larger and further out.
