I recently took an opportunity to be a part of a project that looked like it would be fun. The project involves someone else blogging about a series of events in both an effort to get through a difficult time and the possibility of turning it someday into a book. The project looked and still looks interesting in principle. My involvement is now very much over.
First person or narrative non-fiction is a tricky thing; the writer both has to be factually accurate and give their personal reflections or perspectives on events that have occurred. I read a lot of this type of material. I enjoy reading how a writer views the material, but I trust that the factual details have been thoroughly vetted; including dates, places, and quotes. When those items are wrong or fudged, the entire context of the item as non-fiction is altered negatively.
Fact checking is essential to non-fiction in that events, dates, activities, quotes, etc ... either happened or did not; these things can be fact checked. If a person is misquoted or something is listed as having happened that did not it is a real problem and not a minor deal.
Perspectives are what the writer feels, thinks, believes, etc ... about the items that can be fact checked. Things either happened or they didn't. How the writer feels cannot really be fact checked because that is the point of the non-fiction ... to get the perspective. Opinions or perspectives are not facts and do not get fact checked. By all means a writer should state clearly how they feel about something.
The details in non-fiction matter and are not a small thing.
It is a challenge for a writer of first person narrative non-fiction to get the details right, but it is absolutely essential. If the details are not correct or blur into perspective the validity of the piece as non-fiction begins to fade. Exaggerations or details being a bit fuzzy can occur, but the writer needs to be careful at that point not to state something as factual when it might not be so, otherwise they mislead a reader. There are ways to do this that do not diminish the validity of the piece as non-fiction.