When jotting down ideas, insights, phrases I have only recently begun to mark my own ideas with my initials or tags.

For other older entries I can't always tell for sure if I did a simple paraphrase or summary of something I read. Which means in hinsight I could not use those quotes for writing. And if I paraphrased without the source I can't really tell if I can believe the information or not.

It's an oversight I can't easily fix after the fact.

Yep, a bit oversight.

Pixelpunker wrote:

When jotting down ideas, insights, phrases I have only recently begun to
mark my own ideas with my initials or tags.

Good idea.

For other older entries I can't always tell for sure if I did a simple
paraphrase or summary of something I read. Which means in hinsight I
could not use those quotes for writing.

You could do a Google search on the quotation. If Google comes up with the original source: Fine. If not ... :-)

If you're notetaking for publication you'll probably need to rephrase notes whose provenance is unidentified. Be more strict going forward.

I use my initials in my notes for my own ideas. Copied text is placed in quotes whether or not I cite. I mostly add author and/or URL but not always. If I'm referencing or quoting from a pdf I list the name on my drive as well as its title so I can search for it online if necessary. When notetaking from conversations/interviews I quote what I can, use "~" (or parenthize 'para') with paraphrases.

I don't publish academically but if I did I'd have to keep track of a ton of citation elements like author, title, source, date, page numbers, publisher, URL, etc, using a citation manager.

Before publication I always go through and double check everything by looking back at the original source. It is a good habit, even if you kept perfect notes. You might have misunderstood, or taken something out of context, or mistyped it. There is no way of getting around the need to double-check your notes...