I have not run into the problem of insurance denying charges for things they are supposed to cover, but I have tried (years ago) to cross-reference my medical bills with my EoBs and gave up as nothing ever really matched up.
The actual claims are generated and sent electronically as 837 or 837P formatted garbage (just look up the standard) by all but the tiniest providers but virtually any billing software can generate the equivalent "paper" form.
EoB quality depends on your insurance carrier; if they don't provide a breakdown with the original charge codes and diagnosis codes and a coverage decision then complain and request a more detailed explanation.
The most confusing part is the adjustments; every year the insurance companies and service providers in the U.S. waste a horrific amount of time and effort negotiating adjustment (discount) rates per insurance carrier (insurance always pays less than face value) and charge code. The provider picks prices that give them an overall net positive revenue given the set of adjustments from their (predicted) patient population and corresponding insurance carrier spread, so none of the prices or adjustments actually make any marketplace sense.
If you end up having to fully pay a bill that insurance won't cover, try to offer the provider ~50% and they'll be pretty happy to write off the difference since they wouldn't get much more from insurance. There are also often payment plans and other assistance available if you ask the billers.