When all the tenses basically mean the same?

Hi. Please help.

1) For the three sentences below, I feel all three say basically the same thing, although we may see sentence a more than the other two. What do you think?

a) Sometimes when I am talking with them, I hear myself talking about things I hadn't planned.

b) Sometimes when I am talking with them, I hear myself talking about things I haven't planned.

c) Sometimes when I am talking with them, I hear myself talking about things I didn't plan.

2) For the two sentences below, I feel there is no difference, both indicating cessation of people getting into the place before the time of his departure. For sentence a, I feel, even though past perfect continuous is used, there is no sense of people (people's ??) getting into the place past the time of his departure (since there is what I think the adverbial phrase "Prior to his departure" and when you read that with the rest of the sentence, it seems to show that he wasn't there to let (permit) anyone into the place after his departure.) What do you think?

a) Prior to his departure, he had been allowing people into the place.

b) Prior to his departure, he has allowed people into the place.