I guarantee you that you are missing stuff off the the form because it is normal to you, and you forget that it is not how most families live. try to spend some time with a child of the same age and gender, and you will see what I mean. I'm 'lucky' - my boyfriend has an NT child the same age as DS1 - the differences in concentration, comprehension, organisation, physical dexterity and environment-awareness are made all the more apparent by the lack of difference in intelligence.
DS1 has ASD and ADHD, both of which carry the stigma of being "made up" but his lavck of concentration and short term memory are disabling him! When I compare him to DSS (which as they are the same age and academic ability, with a v similar upbringing, I feel entitled to do) the 'gaps' are clear .... but if I didn't know DSS I wouldn't be able to 'see' them. they would have remained invisible.
You need to get some 'buzz phrases' into that form.
"Unlike other children his age" and "Because of his condition" and "this affects him because..."
You will repeat yourself endlessly, don't expect them to treat the form as one thing wo be read as a whole, ythey treat it as columns in a newspaper, not necessarily related. Write it as though the reader has an IQ of 75. And, when they ask you how long it takes him to do things, make sure you put how long it would take if you weren't helping him, because NT 12 year olds do not need help for anything at all.