Greetings Yuna,
For the validation it's ok in general the way you did it, but I have a couple questions, concerning the bone test sample. Specifically, did you use different sizes, with emphasis to small ones and also, did you simulate real scenario?? Meaning did you place a small bone (more importantly) intentionally in an end product (chicken breast and run it through the X-ray ? And one of the best tests would be to take a chicken breast that is higher than the average weight / size and place in an as small as possible bole in the geometrical center of it.
For the monitoring / verification there are no specific rules, but I have seen 2 common practices, both deriving from risk assessment. First and more robust is to pass a sample every hour of production (it also ensures that in case you have a problem you won't lose an entire production, but only an hour's worth). I have found as well as been informed that testing in less than an hour makes it very tedious and taxing during the production and there is no actual gain, even though there is no limit in food safety!!!
The second (if the risk assessment "allows" it) is to pre-decide that for example you want to have 4 tests in a shift and then spread them evenly in the shift hours.
Regards!