Thanks for this effort. Yes-I have also seen similar other reports in other languages, many caused by the 50-yr jubilee last spring. And when I go thoroughly searching in the attic there may still be some guidebook from those yrs to tell the young people how it all worked and how to do it.

Interesting! Reading this and seeing the evolution of the rail market in recent years, it's actually a miracle Interrail still exists and even has gone digital, despite the justified fear of fraud. 

It seems this also explains the high reservations fees charged in France and Spain, and barriers to reserve them. Pretty curious how the income from Interrail is distributed over the railway operators (an advantage of the mobile passes is - I guess - that they have far better information on the usage in different countries).

That has been explained here also quite a few times-and that as such is in fact the main-even only reason for that travel diary:

Yes, in the past one had to give back-later send, the paper passes to a central office-there was even a kind of returnable deposit for that.

By many able hands and an awful lot of administration these records were accounted for per country-and even in some by company (think of Swiss!). The totals of the 10000s of passes sold were then listed per country-and the income was divided up that way-more or less. Most passes were sold in the north of EUR-Sweden!-and used in the south-in the yrs back then GReece-and ESpana-when it still had loads of trains without much ado. Most used sector for many yrs was Roma-Firenze. This slowly shifts the last yrs. THAT is the very main reason why this new electronic listings replace an awful lot of that work-and old-style paper passes, as long as they are still being sold- are simply forgotten. Statistics: I have studied that- assume the difference will be tiny. Thus it also means that DB cannot take all the money they got for passes sold-a hefty part of it has to be transferred to RENFE and TrenIt. But now that most of the state-national comp.s. do not even sell the pass anymore, more and more its the central office.

Some yrs ago the future of the pass was indeed very insecure-and these cumbersome and nasty RES plight for all those wanted trains have rescued it. Thats why I remain telling that al newbees fall in the trap of wanting just those trains that are hardest to get-they should switch their mindsets and be a tiny little bit more adventurous. Perhaps even-when anyone would still read them-those guideboox could offer ideas for that. But same-same more or less holds for the 1000s who attempt to reach IST/TR over the rails.