How does stat growth work in Final Fantasy (for NES)?

Stats in the original Final Fantasy for the NES have either a 25% or a 100% chance of increasing per level. The thing is, these chances change every level for every class, which I suppose is the reason why that site portrays the stat growth information the way that it does.

The only stat that has a set growth is HP, which usually increases by vitality/4. On certain designated levels, HP will additionally increase by 20-25 points on top of the vitality-based growth, which I will call a "strong" HP growth in my table below.

Addressing your example specifically, here are the stat growths for each level for the Fighter class:

Strong HP growth:
 2-11: yes
12-23: no, yes, yes, repeat
24-50: no, no, yes, repeat

STR:
 2-50: 100%

AGI:
 2-20: 100%
21-29: 25%, 100%, 100%, repeat
30-50: 25%, 100%, repeat

INT:
 2-43: 25%, 25%, 100%, repeat
44-50: 25%

VIT:
 2-31: 100%, 100%, 25%, repeat
32-41: 100%, 25%, repeat
42-50: 25%

LUK:
 2-31: 25%, 100%, 100%, repeat
32-39: 25%, 100%, repeat
40-50: 25%

As you can see, the Fighter will gain strength every level, but other stats have "loops" of percentages that they will increase by.

Source: https://gamefaqs.gamespot.com/nes/522595-final-fantasy/faqs/57009