[FabHK]

Even with equities, things are not entirely trivial.

A few examples: Some stocks trade in one currency, but pay dividends in a different currency. Some stocks go ex-div before the dividend amount has been determined (e.g. in Japan). Stocks trade on certain days, and trades settle on certain days, and they might be subject to different holiday calendars. Corporate actions are not entirely trivial, either (with rights issues, you need to issue two temporary securities for accounting purposes, etc.).

[dabauws]

absolutely - and there's more too, at least when it comes to historical & live data for stocks.

for example: stocks have multiple 'prices' - a bid, ask, last, mid, vwap, twap, etc. a stock's historical 'close' price can be split-adjusted, dividend-adjusted, unadjusted, split and dividend adjusted.. and more. a stock's ticker can change to a ticker used before. a stock can change ticker, but maintain a CIK identifier; a stock can change a CIK identifier, but keep the same ticker.

[mhh__]

Honestly I don't find most adjustments that complicated as long as you think about it economically rather than pulling a formula out thin air e.g. think about how you arbitrage it if it wasn't adjusted.