Hi Martin
I had my probation inspection a few weeks ago and was told the same thing - 3 different properties. It's worth contacting your inspector to see what he wants because my inspector didn't need 3 properties - he wanted to see me working on 3 different appliances (I had 2 boilers, ILFE and cooker) and his view was that he'd rather spend more time talking to me about the individual jobs (they were appliance services) and general gas safety than driving from place to place in the van!
Give the Gas Safe appointments team a call and ask if the inspector can call you and then you can sort it out with him. Whereabouts do you live, by the way? The instructors cover a large 'patch'. If you're based in southern counties, you might have the same one I did. good luck, let me know how you get on