[MileHi]

I never found where it said what the letters indicate.

[WaltStuart]

On one of them, the first one, I think—you had to click on a button near the top but under the listing of the TYPE indicator. The link I posted via duckduck spells it out somewhat.

[WaltStuart]

Assertive (-A) individuals are self-assured, even-tempered and resistant to stress. They refuse to worry too much and do not push themselves too hard when it comes to achieving goals.

Turbulent (-T) individuals are self-conscious and sensitive to stress. They are likely to experience a wide range of emotions and to be success-driven, perfectionistic and eager to improve.

From this link:

https://www.reddit.com/r/mbti/comments/3hxaqn/what_is_the_a_t_appended_to_the_mbti_types_on/