Most of the edges entities in STEP file ends with "T" or "F", like that:
#216 = EDGE_CURVE ( 'NONE', #244, #151, #19, .T. ) ;
I know that "T" means "true" and "F" means "false", but I don't know the explanation of that.
Can anyone please explain to me what is the difference if the edge ends with "T" or with "F"?
Sadly I did not see an answer to what the T and F are beyond what you have found already, but there are a number of STEP related links from these two NASA links which look promising: