I'm aware of the differences as I regularly kept an eye on them during my time as a rep
Good explanation for others though.
What I've seen happen, not as much these days but still happens at some TOCs is that they will cancel the booked diagrams with 72 hours notice and extend the day with the exact same content of work but with an additional trip to somewhere for an extra 2 hours. This is no good for childcare, for example if I'm booked 0600 - 1430 but they've cancelled the job and forcefully extended it by another 2 hours has caused problems for picking up children. Reason for extension? Shortage of staff. Not engineering work or diverted trains but because the company are short. Without sounding abrupt, a shortage of staff is not a guards, driver, station staff or other front line grades is not our problem, we aren't responsible for recruitment and established numbers and I should not have my booked hours forcefully extended for this reason inserted with compulsory overtime with minimal notice. I don't mind working overtime but it has to be a on mutually accepted basis (exclude spare movement). With ATW wanted to have a maximum day of 11:30 hours to this extended working is too much, open to abuse, especially on 100+ stops a day, it's a fatigue risk IMHO.