People who respond to conversational gambits, summarize what they said before if asked again, and provide recap of conversation that is past.

We begin with the idea that each person comes with his own table of things to say:

"Farewell"
A person has a table name called conversation.
Instead of asking someone about something:
   let the source be the conversation of the noun;
   if topic understood is a topic listed in source:
      if there is a turn stamp entry:
         say "[The noun] has already told you that [summary entry].";
      otherwise:
         now turn stamp entry is the turn count;
         say "[reply entry][paragraph break]";
   otherwise:
      say "[The noun] stares at you blankly."

For the sake of simplicity, we'll conflate asking and telling here, though it would certainly be possible to have a more complex implementation if we want the characters to be told things as well.

Instead of telling someone about something:
   try asking the noun about it.

Now we might want to add a recap command to review conversation that has already occurred.

Definition: a person is other if it is not the player.
Understand "recap" or "recall" or "review" as recalling conversations.
Recalling conversations is an action applying to nothing.

Since we've been recording the turn count of each conversation bit, we can even present these in order by sorting the tables first.

Carry out recalling conversations:
   repeat with speaker running through other people:
      let source be the conversation of the speaker;
      sort source in turn stamp order;
      say "[The speaker] has so far told you: [line break]";
      let index be 0;
      repeat through source:
         if there is a turn stamp entry:
            let index be 1;
            say " [summary entry][line break]";
      if index is 0, say " absolutely nothing[line break]";
      say conditional paragraph break.

Now it remains only to create a couple of characters and provide them both with something to say:

The Farewell Bend Cafe is a room. "Beautiful Farewell Bend, Idaho -- or is it Oregon? An almost-abandoned truckstop, in any case, on one of those interminable American east-west highways."
Tina is a woman in the Farewell Bend Cafe. The conversation of Tina is the Table of Tina's Chatter. "Tina the waitress is slowly pouring coffee from the pot with a black neck into the pot with an orange neck."
George is a man in the Farewell Bend Cafe. The conversation of George is the Table of George's Chatter. "There is also a large man at table five. The tattoo on his arm says George. For the moment we will assume that it is his own name and not someone else's."
Table of Tina's Chatter
topicreplysummaryturn stamp
"aasvogel""'Oh, it's a vulture.'""that an aasvogel is a vulture"a number
"acaudate""She shrugs, mid-pour. 'Means something doesn't have a tail.'""that acaudate means 'tailless'"--
"absorptiometer""'It's a thing that measures the solubility of gases in a liquid,' she explains gently, as to a child.""that an absorptiometer measures solubility of gasses in a liquid"--
Table of George's Chatter
topicreplysummaryturn stamp
"baccaceous""'Something that has or bears berries,' says George, without looking up.""that baccaceous means berry-bearing or berry-like"a number
"bagheera""'Oh, that'd be a velvet-like textile.'""that bagheera is a velvet-like textile"--
"balistarius""'That's a crossbow-man,' George replies instantly.""that a balistarius is a crossbow-man"--

A word of warning: this system does assume that every person in the game has a conversation table defined. If that were not the case, we would have to be a bit more careful.

As always, we can override specific words, too:

Instead of asking Tina about "advertisement" for the first time:
   say "Tina looks embarrassed. 'Of course! I almost forgot.' She hands you a brochure.";
   move the brochure to the player.
The encyclopedia sales brochure is a thing. The description is "A glossy flyer indicating that you can receive a free Volume A-Aalto of the New Idahoan Encyclopedia Set if you send back the business reply card, and then have the option of purchasing the remaining volumes at a very very reasonable price."
Test me with "recap / ask tina about aasvogel / recap / ask george about baccaceous / ask tina about absorptiometer / recap / ask tina about advertisement / read brochure".
Test me with "recap / ask tina about aasvogel / recap / ask george about baccaceous / ask tina about absorptiometer / recap / ask tina about advertisement / read brochure".
Farewell Bend Cafe
Beautiful Farewell Bend, Idaho -- or is it Oregon? An almost-abandoned truckstop, in any case, on one of those interminable American east-west highways.

Tina the waitress is slowly pouring coffee from the pot with a black neck into the pot with an orange neck.

There is also a large man at table five. The tattoo on his arm says George. For the moment we will assume that it is his own name and not someone else's.

>(Testing.)

>[1] recap
Tina has so far told you:
absolutely nothing

George has so far told you:
absolutely nothing

>[2] ask tina about aasvogel
"Oh, it's a vulture."

>[3] recap
Tina has so far told you:
that an aasvogel is a vulture

George has so far told you:
absolutely nothing

>[4] ask george about baccaceous
"Something that has or bears berries," says George, without looking up.

>[5] ask tina about absorptiometer
"It's a thing that measures the solubility of gases in a liquid," she explains gently, as to a child.

>[6] recap
Tina has so far told you:
that an aasvogel is a vulture
that an absorptiometer measures solubility of gasses in a liquid

George has so far told you:
that baccaceous means berry-bearing or berry-like

>[7] ask tina about advertisement
Tina looks embarrassed. "Of course! I almost forgot." She hands you a brochure.

>[8] read brochure
A glossy flyer indicating that you can receive a free Volume A-Aalto of the New Idahoan Encyclopedia Set if you send back the business reply card, and then have the option of purchasing the remaining volumes at a very very reasonable price.