But does it matter? if they are not 'phenomenally' gifted then surely they are just bright as a button but within the normal parameters of being so? And that's fine, lovely, something to be proud of, something to enjoy, but hardly newsworthy or deserving of some special status. It doesn't require anything from the parent, or from anyone else for that matter, so why the desire to put a label on the child?
My eldest could do things like recognise/say all the letters of the alphabet and 'read' car number plates at 2, but these were games we'd learned together, they were set party pieces if you like. He could put two words together at 13 months, make actual sentences at 15 months, (that was just something he did by himself, I didn't consciously try to 'teach' him that any more than we all try to 'teach' or children to speak). He had a list of well over 100 words by about 12-13 months, memorised quite long and complex pages of text from his story books at 2.5 (he was definitely memorising, not reading) indeed he memorised several whole books and use to 'read' them aloud to his baby brother. And he always had a remarkably advanced vocabulary compared to his peers.
I wondered if he was extraordinarily clever, but he really wasn't - he just had one or two particular skills which he enjoyed developing. But by the time he was five or six he was merely the right side of average. We had no particular worries about him but he certainly wasn't massively advanced in anything - with the exception of perhaps vocabulary.
He's an adult now and I can say that although he is bright enough and has a degree, he has never particularly excelled academically, in any subject.
I think the education system has done children a great disservice by assigning so many of them the label of 'giftedness' in schools. Like many other things, (impaired vision, being on the autistic spectrum,) there is a sliding scale of affectedness and the people at the bottom end of it barely warrant mentioning, while the people at the extreme end of it are usually quite seriously afflicted by the traits that come with the label of giftedness, as much as they might be blessed by them. It's not something to wish on your child lightly.
The fact that you have already planned to home school suggests to me that you have decided ahead of time that you will have a child who is super bright; it's as though you have desired some kind of 'otherness' upon him. If your child is bright and inquisitive and quick to pick things up, then that's wonderful and just be content with that. Don't rush to turn it into a Thing, for Gawd's sake.