Yes, that is right. But parents have the legal right to have the school they name specified on the statement pretty much regardless.
There are one or two rules that will prevent them from naming a school that is full, but they are rarely applied as they are hard to win and it will usually only be the school objecting, not the LA, which makes for a weak case.
In terms of the law, a class is allowed to go over the maximum number of children for a child with SEN who's parent has named the school for their child.
Generally, the school will argue 1)that admittance of that child will risk the education of the other children (almost never won as the statement 'should' state all the support that that child will need) 2)That there isn't enough space for an extra child (Almost never won as the LA will just tell them to move a cupboard or swap classrooms around) 3)That is is unreasonable use of public expenditure (only won if it will cost the tax payer more to place that child in THAT school rather than another - rarely won. It will cost the SCHOOL more, but not the taxpayer as that support will cost the same wherever the child is placed).
Having said all of that, you have to consider whether you would actually want your child to go to a school that kicks up a substantial fuss to their attendance, and whether or not you would want your child to go to a school where the leadership is so weak they don't even attempt a fuss that will put demands on their budget and remove provision from their current children.
The systems are always going to be against parents and Herts is particularly bad because they delegate so much of the SEN funding so if a school can put off a child with SN they can use it for their vegetable garden to benefit ALL of their children, rather than on a TA to benefit just one.