Exit limits

Can someone explain where the exit limits for the single aisle mainliners come from?

The underlying FAR is mostly 25.807:
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFar.nsf/FARSBySectLookup/25.807

Quoting some definitions to highlight them:

(a) Type. For the purpose of this part, the types of exits are defined as follows:
(1) Type I. This type is a floor-level exit with a rectangular opening of not less than 24 inches wide by 48 inches high, with corner radii not greater than eight inches.

…

(8) Type B. This type is a floor-level exit with a rectangular opening of not less than 32 inches wide by 72 inches high, with corner radii not greater than six inches.
(9) Type C. This type is a floor-level exit with a rectangular opening of not less than 30 inches wide by 48 inches high, with corner radii not greater than 10 inches.

Now, compare A320 and B737 planes.
The measurements from:
http://aviation-safety.net/airlinesafety/exits/
B737 right hand doors are service doors. Lower than the left hand passenger doors – quoted at 165×76 cm, which is 65×30´´. Thus type C.

From:

(g) Type and number required. The maximum number of passenger seats permitted depends on the type and number of exits installed in each side of the fuselage. Except as further restricted in paragraphs (g)(1) through (g)(9) of this section, the maximum number of passenger seats permitted for each exit of a specific type installed in each side of the fuselage is as follows:

Type A……………………………………………………………..
110
Type B……………………………………………………………..
75
Type C………………………………………………………………
55
Type I……………………………………………………………….
45
Type II………………………………………………………………
40
Type III……………………………………………………………..
35

Further:

(7) The combined maximum number of passenger seats permitted for all Type III exits is 70, and the combined maximum number of passenger seats permitted for two Type III exits in each side of the fuselage that are separated by fewer than three passenger seat rows in 65.

What I get for 737-700 is 145 passengers:
55 for each right hand Type C exit;
35 for the single overwing Type III
total 145.

This number I think has been mentioned for 737-700, and also for CS300 (same exit arrangement)

Now, when I count exit limits for 737-800, I get:
110 (2×55) for the 2 right hand Type C;
70 for the pair of overwing Type III exits;
total 180.
The problem is – the exit limit of 737-800 is commonly quoted as 189.

How can 737-800 carry 189 seats? Where do the extra 9 come from?

Now, the Airbus right hand doors are full height – unlike the 737 doors. These doors are quoted as 185×81 cm.
But this means 73×32´´.
Which qualifies as type B – unlike the 737-s Type C exits.
With 1 overwing Type III exit, I get:
150 (2×75) for 2 right hand Type B;
35 for single Type III;
total 185.
Yet the exit limit of A319 with 1 pair of overwing exits is commonly quoted as 145.

Why do not Airbus right hand doors count as Type B instead of Type C like the lower Boeing right hand doors?