N&G - I don't have any personal experience of this & cannot give professional advice (other than knowing from a teaching perspective that it does happen that staff can be unaware that a child has had an "accident"), but I can offer my DS experience with his then new partner's 4 year old son.
Prior to my DS relationship with his mother, the little boy would "retain" both urine & stools, often having accidents at both home & latterly at school. He was increasingly distressed & sometimes in actual pain from impaction; he was "inaccurate" & demonstrated severe aversion to toilets & had done so from the commencement of potty training. Our very first meeting with DS girlfriend & her son was in his second term at school & was a hard weekend for all concerned.
Shortly after moving in together & following advice from a sympathetic GP, my DS supported his new family in clinic attendance (for all) in order to gain insight into the strongly-suspected psychological origins of the issue & to get practical guidance as to how to alleviate & reduce the behaviours shown.
In this case, after further enquiries, it became clear that extreme inconsistency in toilet training approaches from other members of the wider family were the cause. The child had experienced limited, but very negative "training" at a critical time, which had resulted in his all-too obvious fears.
With consistency from all involved, gentle acceptance of "mistakes" & calm, clear guidance... a year on & things were almost what you would hope for a rising 6 year-old. There were occasional errors which were dealt with without unnecessary fuss or comment.
At 8 and a half, he is "reminded" before journeys etc & my now "big" GS is assisting his Mum (now my DiL)& DS in the joys of potty/toilet training my nearly 3 year-old GS.
Hope things turn out well for the little lad & his family.
