This is obviously a fairly big issue. Also, I wrote much of it out of order -- I started out writing (for my own amusement) various interesting scenes and scenarios, and building a story from that, so it was important from the start to keep things straight.
I have a massive file of random notes, several spreadsheets, and a working file of notes where I jot ideas down....”
Hopefully, nothing I write is offensive; not my intention! If you are writing the novels for yourself, go for it. If, however, you want to sell these one day, you may have problems. Obviously, readers want to be satisfied. You are selling a polished product to them. They want to be able to figure out the logic, as the story unfolds. Foreshadowing gives them the clues they need, based on previous information you tell them, to at least guess at the outcome of an event (or a series of events). Without continuity, readers will be confused; i.e. they may feel they are not be able to form an educated opinion of what may result from said buildups. These may result from continuity issues (i.e. problems with inconsistent information you relay, over time, to the reader). Saying one thing in book 2, then contradicting it in book 7, will confuse the reader.
If you have not researched means of continuity management for series, give it a try. I gave some examples. Timelines are another, but that's more a topical one. Research "series grid" and "character map novel writing." Look up "character charts" too.
For more on the literary bible,
https://en.wikipedia.org/wiki/Bible_(screenwriting)
George Lucas kept one of these for Star Wars. He calls it his Holocron (a digitized version of his "bibles").
https://en.wikipedia.org/wiki/Star_Wars_expanded_universe#Holocron_database_and_canonicity
I'm tackling problems with some continuity myself, in my proposed series. I am working through them now, before I start writing word one, of book one.
I have a lot of research and pre-written dialogue too. I have databases for character names, character bios, magic system with spells, potions, and so forth. I have loads more databases of research, all digitized. The problem is, how does one piece it all together, not just for one book, but for an entire series? This is where these continuity tactics, mentioned above, matter.
Here's another issue, hopefully one you managed.... Do you have a data management plan; i.e. a plan to have backups of all your databases, writing, books, and so forth? Do you have more than one copy saved (e.g. one to computer, one to thumb drive, one to cloud storage, one to CD/DVD, other)?
Series writing requires a lot of pre-planning, if continuity is a concern to the writer. I started my project, day one, August 14,
2017 2018 (Monday). Eight months in, I am almost ready to start writing. I had to teach myself how to write novels then how to write a series of novels. My fictional universe spans 4 eras and 30 years. Potentially, I see 17 books in the series. If I cannot land an agent, and a sale, for book one, I won't write another book. This is all a learning process for me, and a personal challenge to use my formal education in project management and other things; i.e. I want to see if my organizational skills are up to par. Writing a novel series reminds me, very much, of writing a Federal U.S., research grant. If you don't deliver a perfect proposal, you won't get funded (i.e. an agent, a sale, fans, and so forth). Well, Federal grants have to be this way; maybe not so much books, but close to it!
H G Wells would have been impressed. 
