With some lines there are less reporting points than stations meaning that they'll check how late a train was at the nearest reporting point to where you alighted and if the train made up five minutes between where you alighted and it's next reporting point then they could say the train was 57 minutes late, when you say it's 62 minutes late.
The legal requirement is 20% of a single ticket for a one hour delay or 10% of a return ticket for a one hour delay. Most TOCs are a lot more generous than this, until recently Merseyrail paid out at the minimum despite most stations having at least one train every 15 minutes, which made them look a bit mean compared to other TOCs.