[CQ-Contest] He send didn't send his callsign

[Bill Parry]

The discussion of sending the other stations call sign (a real good idea)
reminded me of something that happened to me several times.

The station answered my cq with his/her call. I responded with his call and
my exchange. The station responded with my call and his exchange without
sending his call as a part of the exchange. This happened three times. One
time the responding station just sent the last three letters of his call as
part of the exchange.

This was a problem a few years ago and I thought it had stopped. Since it
happened more than once, I'm sure that it must have happened to others. If I
accept the exchange this way, he and I both benefit from a shorter exchange.

So what is the correct response? Have him repeat his call? (I already know
it and it is in the computer). Have him repeat the whole exchange? Ignore
it, I teach physics not ethics anyway?

Bill, W5VX