If one downloads the quotes directly from the exchange site (in my case
www.nseindia.com), then in most cases prices are not adjusted for splits,
bonus, right issue, and even symbol change. If you are following a handful
of scrips, then adjusting things manualy is not a problem, but in case you
use scanner to search for specific patterns, then updating all the scrips
manually and especially historical data of decades is next to impossible.
This can be done with a plugin that reads details about splits, bonus,
right issue, change of symbol, from a cvs file and makes appropriate
adjustment. This pluging might be in line of quotes updating plugin, you
need to write new functions.
There is a software that claims to do similar things. DE Pro from
http://www.investbulls.com. They download EOD data from exchange website
and the cvs file for splits, etc., from their site and make adjustments in
the data.
Also, a scanner to scan possible dates of splits, etc., based on difference
in prices of subsequent days is going to be a great thing.