Hi Alek,
There are only a few minor changes in the revised edition of the guidebook. The main changes are:
Sub-sector Comic Tree was updated (photos, grades, comments)
Sub-sector Big Shadow was updated (info about rebolting)
Besides that, a handful of route grades or descriptions may have been updated. If you have the 1st printing of the 2019 guidebook there is no reason to buy the revised edition.