.... Reading 29F200 flash memory (sop44) ... I'm getting different read every time, also when verifying ...
I have no problems with 29F100s and others in that series type. Have you looked at a memory dump? How many bytes look wrong?
There's usually huge chunks of FFs or 00s. Is it very slow memory? Maybe CS etc is too fast?
I've had similar problems in the past and have to ADD pull-up resnets on the address lines, and pull-dn on the data bus. app 33-100K
I even made a custom adapter with selectable jumpers. If you have an oscilloscope, you'll see immediately if all the address / data lines
are "clean", or if there's loading / timing issues.