Hi and welcome to YT. Glad that Winston has found you. Poor baby has been thru the ringer. I would make sure to have some Nutrical or Karo syrup around in case he starts to get a little shakey from hypoglycemia from not eating.
I would just forget about trying to get information from the previous owners and just start your own regime with Winston. At this point, getting him to eat is more important. Maybe try some boiled chicken and rice and slowly find a food and mix it in until he's totally on it. At 1, he would be considered an adult, but I would probably still give him some puppy type of food as it doesn't sound like he's gotten very much proper nutrition. Puppy food is higher in fat, proteins and vitamins. I wouldn't keep him on it for too long but maybe for a short while.
I feed mine Stella and Chewy's raw freeze dried. It's convenient and good for them. I have probably feed them 10-15 different types of foods and this is the one that they consistently eat which is a good thing for the convenience when traveling.
Good luck and don't be afraid to ask something.
