I'd guess that depends on how/why new ones are made. If there's, say, a PoE 2, I could see a second book coming that further expands lore in preparation for that. In which case I can't see it being complimentary for backers of the first one.
That's why I ask...
But reading again.. "We hope that you can help us illuminate the contents of many more volumes in the years to come." COULD mean that there are plans to few followups.
But if volume 2 should have something with planned expansion then I hope it would be complementary for all of us who have the first expansion in our tiers..