Advice?

it sounds like yes, that would have happened........

this would of been down to the basal dose largely.......

how are his levels overnight without any quick acting bolus working.....?

If he's dropping that much overnight without any bolus insulin that's a strong indication that his basal is set (ridiculously) too high.

Glucometers can't account for all variables and certainly not human error. They also can't account for the honeymoon phase assuming your son's pancreas still has some ability to produce insulin.

@KW's_Mam Had he had a hypo earlier in the day? The high in the evening could have been a rebound as the liver naturally dumps glycogen into the bloodstream after a hypo, and then later, when the liver needs to replenish the spent glycogen, it causes a drop in BG. This is something worth looking at before correcting a high, as overcorrection is possible in this scenario. If I am correcting high blood sugars within about 18 hours of a hypo, I often consider halving the correction dose.

Hi

Correcting high bg levels late evening is always difficult esp if also going to bed and being worried about going low.
Although the basal might be a bit too high and need reducing, some foods and the way they get digested, can cause a high bg for a couple of hours and then bg may start to drop. Did your son make sure that his hands were clean and also wiped on a towel that hadnt been contaminated with something sugary? Did he touch something that might make the bg test a bit dodgy? Whenever I get a high bg on a bloodtest strip, I usually double check again using another strip just to make sure.