I have heard of a 3 day rule (rather than 4) but after first tastes we didnt really abide by it any more especially as there is no history of allergy. I introduced meat in casserole/stew type meals so the meat was mixed with veg.
I think the 3/4 day thing comes from when babies were weaned earlier than 6 months, and I can see why you would want to be careful if you have allergies in the family.
But with my 2, I did baby led weaning, so just onto family food at 6 months (minus salt). Try not to worry too much about iron levels, they do start to reduce at around 6 months, but it's not like it's going to disappear over night.
After first tastes we just went for it because i figured my DS is a hungry little monkey who will try anything and eat almost everything. He tries from our plates if it's food that's appropriate for him (he's 6.5 months). When i introduced fish and meat i did it alongside foods i already knew he liked. But today we went for tomato, yellow pepper, onion and mushroom pasta - none of which he's tried before - and he was more than happy.
No history of allergies here though and DS has moved really quickly onto 3 (big!) meals a day.
Yes the introducing foods slowly 1 at a time was when most babies were weaned before 6 months. I have eczema but was told by hv etc that it really is only if you have food allergies in the immediate family that you need to be cautious.
Also doing blw so just give him some strips of steak, chicken etc. They just suck and gum them but that is enough to get the good stuff.
i had to do this with my last charge (no allergies just parents didnt like to hear my opinions), it was a nightmare, one new ingredient every 3 days and with jar food which was hard as jars gen had a lot more ingredience in like tomato and onion and if he hadnt had that he couldnt have the jar so very slow process. he did have chicken quite early on though with apple and carrot (jar).
why dont you give him some chicken (which is a great first meat) with some carrot and pear (which sounds gross for adults but a little apple or pear is quite nice to mix with savoury) if you want to stick with one new thing every 4 days, otherwise if you feel he seems to be allergy free, just give him what you have next (and puree it if you are doing that with your bubba)