The clear HPI report would be what you need. I think you say that it was clear when you checked it in 2016, and that now it shows that it was clocked in 2012? And have you sold it to a trader or to a private individual as a 'trade sale'? TS may just want to go through the trail, they may want to do more. But, having had a visit from them a few years ago, the picture they build up of you during your chat is likely to influence your future dealings with them. So get all the advertised mileages on your forecourt up to date, don't advertise something with 50000 miles if its done 50551. they want accuracy. And get all your paperwork in order so they can see all your cars advertised have current MOT's.
Dont advertise with full service history unless theres a stamp there for every year (unless the manufacturer says differently)I'd also suggest a quick check that they all start and no bulbs have blown. If thy think that your cars which are currently available for sale are all good, they will look at you far more positively and listen to your side of the story.