Only if specified in writing however I honor any referral for years!

I don't really know the answer to this.

Depends what the written referral agreement stipulated.  No written agreement - no fee due...

I agree with Paul and I too honor referrals for years. The connection would not have been made if it wasn't for the referring agent.

I forgot to mention that perhaps the reason why the agent referred it to multiple agents/brokerages is because they wanted the family to decide which agent they'd prefer to work with.  That's not unreasonable and perhaps it was the family that stated they wanted to interview more than one agent.  Many agents offer more than one vendor when asked for recommendations, why shouldn't we expect referring agents to do the same?

Hmmm... that's a bit of a tough call.  If the agent is a friend or relative of the family, they're likely to find out and expect that referral commission.  You bring up a good point... referral agreements should have deadlines by which they are no longer in effect unless renewed by all parties.  Even new home builders have deadlines by which the prospective buyer must buy or you get no commission.  Hate to say it (and I'm not a lawyer) but I'd say the referral agreement is still in effect.  Only way I can think of that you may not have to honor it is if you are no longer with the same brokerage since it's the broker who is supposed to honor it.