CAESSR may be as much in the dark about Barney's medical history as you are I'm afraid - dogs are often surrendered to them with little or no information depending on the circumstances - in some cases they are stray dogs :/
I am aware that the team at CAESSR have some "challenges" with IT so it may be easier to call John or whoever your point of contact is to discuss his condition - hope you get some answers soon
I've not had a dog suffer from colitis but have got a rescue cat who developed it about 6 months after she came home - she was a stray handed in to my vets, who then asked me to take her rather than putting her into a rescue - it seemed to coincide with her starting to relax and settle in to the house. She's also had a recent bout of pancreatitis which was definitely my fault ( let her have some sardines in oil) so I now know that she has to have a very simple / plain diet. My preference would be to have her on a good brand/high protein food but actually she thrives on the cheap stuff
Also had a cat come home (age 12 weeks) with giardia - now that is unpleasant diawotsits
- then picked up campylobacter about 12 months later. She is also on a simple diet and will not eat human food, thank fully! Both conditions took some identifying but we're easily treatable.
Pearl cannot tolerate any of the better quality kibbles, she is predominantly raw fed but I do move her on to kibble while we are on holiday in the caravan. It appears that anything over 30% meat protein upsets her digestive system and I have to confess to feeling guilty that's she's on Vitalin Senior when my budget would stretch to much better quality food
I suppose what I'm trying to share is that it can take a long time to establish what works well for one of our furry friends and sometimes it's not the obvious choice! Wise decision in my view to get him checked. I hope it rules out anything more serious than an imbalance in his gut,
Jayne