Primary source

The original document rather than anyone's summary of it: the filing, the transcript, the regulation, the price data.

For a company, the source stack is the set of documents worth assembling before starting: several years of annual reports, the last eight quarters of results and transcripts, the shareholding patterns, the credit rating rationales, and whatever the regulator publishes about the sector.

Assemble it first, and the analysis goes faster afterwards.

As summarisation has got cheaper, the habit has become more valuable. A generated summary of a filing is fluent and fast. It's also confidently wrong in ways that are undetectable without the original open beside it: a figure from the wrong year, a segment misattributed, a caveat dropped. Any number reaching published analysis must therefore be traceable to a document a reader could open and check, and any number that can't be traced doesn't go in, however plausible it looks.