There were certainly syllabus differences. I was the first year of GCSEs.
In one of my first A-level French classes, we went through an old O-level paper to get us back in the swing of things. There were things we'd never touched, like the subjunctive.
Some years later, I did an MSc conversion in Computer Science, and there was one assignment in graphics where you had to code the graph of a differential curve - I could do the coding, but I first needed to understand what I had to code, and I didn't know. I had the GCSE maths which had been the minimum entry requirement, but that had been based on O-level.
I would expect things to have changed since the 1980s and '90s, mind you. There should have been syllabus changes in a quarter of a century (it was a world without mobile phone or the Internet.)
I do think school-level maths is probably easier with metric currency and measurements. When you're learning arithmetic it must be easier with everything being decimal, rather than 12d in a shilling, 20s to £1, inches, feet, yards and so on. I know you get used to it, if you're dealing with it all the time, but it must mean there's a steeper learning curve, which just complicates things like learning how to calculate areas and volumes or interest rates or whatever.