Leonardo Express from Fiumicino to Termini
 

Following advice on my previous thread, I decided to purchase the Leonardo Express in advance. I was surprised that the date (7OCT) was not available on the Leonardo website but was available on Trenitalia so I purchased the ticket (after confirming by chat that there is availability on other sites). I selected the earliest time that I thought was reasonable. But I was surprised to receive the ticket with the information that 1. the ticket does not need to be validated...and 2. changes are allowed only up until 11:59 pm the day before. I understood that the ticket is not train specific and can be changed for a later train. Did I purchase the wrong type of ticket?.

You may find answers to your question in here:
https://www.rome-airport.info/leonardo-express.html

Let's call things by their name: Buying in advance the ticket of a train that has no discounts and that can't sell out is just silly. And the advice you received on the other thread is wrong. Internet at its best...

Especially when there is free wifi at the airport and one can buy the tickets via app while walking towards the airport train station.

A little research would have prevented such mistakes, it would also explained that:

1. regional train tickets purchased online never need to be time-stamped. The reason is that the countdown to use such tickets starts with the departure of the "booked" train and not with the time stamped by the validation machine
2. The LeoEx is a first class Regional train, so a ticket purchased on line can be used on the "booked" train and on any LeoEx departing within the following 90 minutes. Another reason to get tickets at the airport
3. You don't change a Regional train ticket. As long as it hasn't expired, you can freely get on another Regional train making the same route on the picked day. The "same route" means you can take a LeoEx to Termini, not the FL1 to Roma Tiburtina station. Even if the FL1 is cheaper, it departs earlier than the next LeoEx and you have discovered that the FL1 will take you closer to your final destination. Or that all trains departing north from Termini call at Tiburtina after 10 minutes. Another reason etc. etc

ps There is no "Leonardo express website"; it's property of and managed by Trenitalia.