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As controversial as it sounds, there are so many things an inflation calculator doesn't compute that it's useful (with several pinches of salt) over a 15 year period – over a 145 year period it's pretty much just a random number. Like any statistic, you'll see it cited by organisations when it suits their agenda but not when it doesn't.
If you put the average unskilled wage in 1880 (~£30) into that same calculator, it'd probably come back with ~£3,000; an unskilled worker today earns in the mid £20,000s.
In other words, £1.65 today may well be 60% more than 1p in 1880 using raw inflation, but the amount of earnings you'd use to buy a stamp (or the amount if minutes you worked to buy the stamp) will be significantly higher
The inflation basket also doesn't take into account direct taxes like income tax or NI, which matters if you're using money to represent how many seconds/hours/years you've had to work to buy something
These are only a few variables... in 1880 the idea of unearned income (dividends, rent, interest, or more recently benefits) was unheard of to all except the super rich; unemployed people in 1880 couldn't comprehend the idea of being paid to sit at home! The tax burden is totally different and has shifted differently depending on demographic. Also the personal burden is higher – more people today being forced to pay for fuel duty, insurance or even private healthcare, which isn't really discretionary even if it's technically so.
There are hundreds of essays written on this, probably thousands. It's an interesting read if you are ever interested 👍