If the bolt does not have the same serial number as the rest of the rifle there is no guarantee that the gun has been proofed as a whole unit. In theory there should be proof marks on the barrel, action, bolt handle and bolt head.
All these are pressure bearing parts and can of course be changed independently of each other.
It is not unusual to find a miss matched rifle ie different serial numbers to the bolt and action but providing there are proof marks on the individual components then it is accepted that the rifle has been through proof as a unit.
I have also seen fully matched rifles that only have visible proof marks on the barrel and action with nothing visible on the bolt but as the numbers all match it is accepted that the rifle has been proofed as a unit.
There are in theory some very heavy fines for selling an un-proofed firearm in the
UK
, up to £1000 per transaction. From the description of your rifle and piece of mind I would suggest that you have your rifle checked to ensure that the bolt was properly "fitted" to the rifle and not just thrown in, get the headspace checked and then submit it to the proof house, that way you know that is safe to shoot and it fully complies with the UK proof laws.