JK Rowling keeps coming up as an example - who else remembers the time when one of the Harry Potter book's release date was postponed for months and months and months while she rewrote huge chunks of it? She did have the whole series planned in advance, but was still willing and able to adapt that plan, even though earlier books in the series were already published.
She started Harry Potter in 1990 and the last book was released in 2007. About 17 years for 7 books (with time off, looking for a publisher on her first book, and so forth). I think I read, months ago, she wrote the first book between 1993 and 1996, but I may be mistaken. So 1993-2007 (14 years to write 7 books @ 2 years/book average). I suspect she created a lot of the content (characters, spells, researched a lot of things, developed the series into 7 books, and what not) before she started book one (1990-1993).
She said in an interview, maybe it was the Oprah interview (I forget), she had an idea where the rest of the books were headed only after she finished book one. This does not suggest she knew everything at that point. She did not have the series planned out in advance (i.e. before writing book one).
As you note, she had a lot of re-writing and delays. Were these pantsing issues? Dunno. You can Google "Harry Potter plot holes" and see her series was not without flaws. Could she have better managed these holes by planning better, before starting the series? Dunno.
For my series/project, I developed custom tools to help me manage the promises I make and making good on them. This is a recurring message of Brandon Sanderson (in his online videos), and I agree with it. I'll have the outline, of every book, complete before I write book one. Each book is a standalone. Continuity, in series, is important (not just in each standalone).
For those who dread potential massive rewrites (and, maybe, re-reading other books in series to get the current WIP in line with the others), potential numerous relays between agent and author with fix suggestions (throughout the entire series), potential continuity problems (and finding them), maybe more planning (i.e. front-loading) is the way to go. Will all, or any, of these things happen if a series is pantsed? No. Can they happen?