Thank you v much prh47bridge for your concise answer.
You confirmed my fears - most likely too little too late?
If there is anything else you (or anyone else) thinks we should / could do based on the below extra info, I'd be most grateful for further advice.
Unfortunately, because (the severity of) this came out only late last year (for goodness sake, DS was only 3!) AND DS has been referred on from one agency to another without actually being formally assessed by either, it is looking like we will miss the deadline.
But I feel I need to do the best for DS. And feel woefully unprepared.
Re. Appeals:
I didn't even know that there were such things as 'infant class appeals' until reading about it on Mumsnet last night.
I assume by inference that there are other grounds for appeal, (such as error?). I presume none will be relevant to us?
Re. EHC:
If DS is diagnosed with social anxiety disorder / reluctant communication (and various associated high sensitivity issues incl. withdrawal and peer interaction), which is the way it is looking, then will it be argued that he doesn't need an EHC plan as this could be dealt with by in-school SEN?
I thought EHCs are hard to get as they involve money flowing from the LA?
In principle I would be ok with this ... if the school were 'a good fit', which we are discovering is fundamental in dealing with overcoming anxiety.
As per our first choice, 2nd closest local school (popular, on cusp of cut-off, probably won't get in on distance).
Our nearest will finish him off - huge challenges, not yet 'under control', being dealt with through hardcore discipline, so we didn't even apply.
Applied to next closest 6.

Any more thoughts most welcome.
Thanks