Firstly I nothing about model boiler testing, I do know about autoclaves but let me ask this question
I buy a Polly kit with boiler today, it comes with a boiler number and a test certificate ? I get it fully assembled and working and get all safety checks etc etc done. I take it to an open day and the boiler lets go due to a mufacturing defect and someone gets seriously injured. If what you say aboput Polly's lack of records is true, rather than them just not wanting to hep you, I would not want to be the H&S manager at Polly when the HSE turn up asking to see;
Calibration records for testing equipment
Training records for the person dong the testing
Records of Tests vs boiler numbers & dates for the Boilers they make