You pass is valid in Estonia. However, that has only been the case since last year, so before 2020 I can imagine he had "troubles” with it in Estonia (and Latvia).

If there were problems in other countries, then please specify in which countries and what kind of problems.

Since that year only the 3 baltic states have been included.

Main problems with travel on IR are:

1.the very hard to get and also expensive REServations fpr Hi-Speed and express trains, with Spain and France topping the list

2.IR is not valid on some railways, this varies enormously per country. This is a heritage from the old days when there were just the monopolistic state-railways and since then there have been many privatisations.

3.passing gates, sometimes easy, sometimes very hard to do-no staff in station, noone to help you with this.

Also in east-EUR it often is simply not worthwhile to travel on IR, as local fares (pay as you go) are still quite cheap.

But this does not mean its all worthless-you have to plan and make more information.