In reply to Some Random Climber:
Not, its not definitive- I'm not sure that Ground Up do any definitive guidebooks.
The reason, I'd expect, is that any guidebook production is very expensive... it's a lot more than just writing the words and adding some lines on photo.
Particularly if you're interested in the lower grades, then get your mitts on the old guidebook!
If you think you need help with finding routes (route description reading is a rapidly diminishing skill amongst climbers) then get both, and with a bit of applied intelligence you'll have a good guide to what Welsh Winter can offer for the few days it's in every year!