No you’re understanding is incorrect. There is a big difference between an expired cheque and a reissued cheque.
If I walk into a bank with an expired cheque, they will not honour it, so there is no risk of 2 people cashing the separate cheques. If I walk in with a valid certified cheque, they MUST honour it, even if someone already cashed the reissued cheque.
You are correct that the recipient could wait ~1.5 years for the cheque to expire and then issue a new cheque, but that’s a significant delay and the estate likely wants to close its books before then.
My wife and I once had enough saved up to buy a used car from the dealership. The sales manager told us their incentives were structured around financing, so paying cash up front wouldn’t count towards their monthly sales figures, and to them it was “useless”.
Ended up financing with an open loan and paying it off, in full, on the first payment. Probably lost them ~$1000 in processing fees but they knocked off another $150 for my first interest payment.