NHBC Standard for this states:
"Ventilation openings should be provided on at least two opposite sides."You have air bricks on all four elevations which is good and better. The air area 6170sq.mm is correct too.
What you don't know is if they are periscoped under the floor and/or properly connected to the periscope ducting.
Asking the foreman, he will tell you they are! He is hardly likely to say anything else even if it is the truth.
The only way you will know for sure is to get a replacement air brick, then smash one out and check yourself.
You should see the top half of the black ducting. You will then need to poke a piece of wire down it and should hit the bottom periscope bend. This will confirm the ducting (to that air brick) has been installed correctly and may give you re assurance the rest have been too.
You need to measure each elevation separately.
If it is 12 metres, 5 vents at 2m centres with the first and last 1m from the end.
If it is 6 metres, 3 vents at 2m centres etc. with the first and last 1m from the end.
Putting a vent under a door means the top of the periscope will be shallow in the floor screed and may cause it to crack, if indeed there is any cover over it at all.
Whilst important, if the air bricks and ducting are not 100% compliant it is not a major issue provided the floor is ventilated to some extent. What it will tell you ios that your new home has been "bodged" in this respect and that other issues may be lurking to be discovered at a later date that may cause you more serious problems.
I know of one Bellway new homebuyer who had his house demolished because the wrong bricks had been used, the mortar used was too weak and the roof had been bodged during construction and then made worse by the NHBC's contractors attempting rectification.
http://forum.brand-newhomes.co.uk/nhbc-warranty/nhbc-hire-cowboy-builders/http://forum.snagging.org/nhbc/2077-nhbc-butchered-my-roof.html#post7909