QI find I have limited access to information where I work (I suspect for security reasons), but the unfortunate side effect is that I sometimes make an error because I don't have all the facts. How should someone with no clout go about trying to change company policy in order to remedy this?
ADetermine what you need, present "need to know" business cases to your boss, and document your assumptions about what to do when limits remain.
The inner game
Look at the information you need, analyzing the situation task by task. Catalog the errors you've made, looking realistically at the root causes. These may include limited information, but may also be due to factors such as simple human error. Be thorough and own up to errors that may have been avoidable so that you can be effective in making a case for needing additional information.
Then restate the situation so that instead of seeking specific information, you're articulating the questions you need to be able to answer. In this way, you open the possibility that other information sources may be able to give you the direction or insight you need.
Be sure that you understand your company's data security policy.
If you're not sure that your limited access is due to security reasons, explore whether there are other reasons, perhaps related to long-standing business processes or old company habits that may be more flexible.
Finally, get a sense of whether you have, in any way, caused any erosion of trust. Likewise, consider whether your trustworthiness may simply be untested.