Quite honestly and to be blunt you are peeing in the wind.
The prosecution has no responsibility to prove the accuracy of the speed camera unless you are intending to suggest it is inaccurate. All they need to do is show that you were detected by an approved device exceeding the speed limit. If you raise a defence that the device was inaccurate the burden shifts to you to prove it. As far as I can see you have not got that far. You are only suggesting that the calibration certificate you have been provided with (which has been provided as a courtesy, not a right) may not be the one relevant to the camera that detected you. To succeed in your defence you will have to prove that the camera was inaccurate, not simply that the paperwork you have been provided with is deficient.
Now a bit about what will happen if you fail. You will be convicted and face a fine of half a week’s income and three penalty points. However, that will be the least of your worries. In addition you will pay a contribution towards prosecution costs (probably about £450) a Victim Surcharge (10% of the fine with a minimum of £20) and – assuming the offence was committed on or after 13th April – a “Criminal Court Charge” of £520. So you face a fine and other costs of well over £1,000.
It seems you were guilty of the offence (nowhere do you suggest you were not). In trying to avoid a conviction using a defence that is almost bound to fail you are risking the fixed penalty of £100 against a fine and costs of more than ten times that amount if you take the matter to court. Of course only you can decide what route to take. I know what I would do in similar circustances.