We have had an MY15 T+ from new and have done about 42,000 km.
I’m a member of Australian Ford Everest Forum and the similar one here in Thailand.
I am aware of that issue and have checked our car a few times including just now…I have never been able to find any evidence of rust underneath the paint similar to what you have shown.
We have been very pleased with the Everest.
The thing that you need to check for is a smell inside the car. If it has one then it’s quite a big job to sort and I had to contribute towards some of the cost. If you want to see what is involved to change all the insulation PM me your email address.
Also check for an oil leak from the rear engine oil seal. Most of the early 3.2Ltr Everests had this problem. Ours was changed at 15,000 km and it’s OK.
You might be better off buying one that was built in 2016 or later because they have sync 3.