Mmmm...except you'd have to look a little closer at their numbers.
For example, if their current YR cohort 62 (two excepted children), but their current Y1 cohort is 58, they could choose to make next year's cohort as follows:
Y1 class
Y1/Y2 mixed class
Y1/Y2 mixed class
Y2 class
Which means that they wouldn't be making additional arrangements, they would just be shifting the children into acceptable numbers.
Also, every area has a natural turnover of children, so you'd have to bear in mind what tends to happen at that school/schools in that area. Is it likely that 2 children could have left that school by July? In which case, again, they could argue that it isn't an issue.
Thirdly, you need to look at the floor space, net capacity, etc. Part of the prejudice consideration for appeals panels for places is looking at the building, to see if it can cope with another child.