I understand your need to be fluffy - I've done it too. It is so frustrating!
Given a choice - forget fluffy, at least to a large extent. As things currently stand, this year's teacher COULD try to argue that it was hard to find the specific information in everything else. You DID tell her, but she could argue she didn't have time to fully take on board a longer letter with vital information smuggled in between apparent 'news'.
You don't want them to have ANY wiggle room here. Last year's teachers who got their backs up - they were even more wrong. You were giving them vital information, in writing. Unless your tone was so terse as to be offensive, they had NOTHING to object to. And by being so touchy about it, they have pushed you into communicating in a far less effective way, in your bending over backwards to not offend.
I'd talk to the school. Especially if they use the argument I just mentioned (I hope they don't but I'm concerned they might), tell them that you were trying to inform them without causing any offence, after last year's school got uppity. But this is YOUR child, you MUST communicate effectively because this is literally vital. So ask them - what would they prefer? Polite and chatty? Or concise but terse? Whatever they say, make it clear that you WILL communicate, in writing, to make sure the information is there.
With the Communication Book we used for difficult child 3, I DID encourage a certain amount of 'fluff'. It did act as a social lubricant between me and the teachers. However, when things were really important, I was concise. I knew that they did tend to 'bleep' over a lot of the apparent irrelevancies I wrote, especially if they were busy, so when I HAD to make my point, I kept it short and to the point.
You're starting over in a new situation - it's really hard to get it right, because "right" depends so much on a lot of things you just don't know about the personalities in this new place.
Do not apologise to them for any of this. Don't even allow yourself to be tempted. They may try to make you feel guilty - don't wear ANY of it. If they try the guilt trip, or try to sidestep their responsibility, come right back to, "This is why we should have had that urgent 504 meeting I requested. It would have prevented so much of this. We now need to move beyond recriminations and get back on track for this child. Mistakes have been made - let's start afresh, all of us, and work as a team to sort out the problems for difficult child. If we work together it will make your job easier; it will make my job easier. It's got to help all of us."
I am wondering, though - a communication book may be a good way to work from here with the school (ask me, if you want more info on how it works). In which case, the 'fluff' level (I do like your description, by the way) can make communication friendlier.
I think last year's school really damaged your confidence as a parent with the right to be respected. Take it back - take back your rights and your confidence. You are a vital part of your son's Learning Team and the sooner the school accepts this, the better you will all get on and get by. Keep reminding them - you are vital to the Learning Team. School, community and family are all inextricably linked. Do not let them isolate you or devalue you.
I'm hoping this school will turn out to be different. They've SNAFU'd once; let's hope it was part of a steep learning curve. Here's hoping this scares them into paying closer attention. Give them another chance but watch them closely. As the old Arab saying goes, "Forgive the man who steals from you, but lock up your camels."
Marg