It sounds like someone was tasked with catching up with all those forgotten during COVID. It's not good that he hasn't been actively monitored, but NHS admin is not good at the best of times, so it really is up to each patent to know what to do, and when. If the patient doesn't want to follow their regime, it's probably quite easy to simply drop off the radar.
He should have had 3-monthly PSA tests in the first year to work out his PSA velocity (rate PSA is changing and how much it fluctuates in his case). If it remained stable, the interval would be increased, but still at least 6-monthly. He should have had an MRI scan each year, so coming up to his second one, and this would include spine if there was pain there, just to be sure it's not cancer.
A rise from 8 to 10 in 20 months might not sound much, but with no intervening readings, you can't tell if it stayed at 8 and rose to 10 in the last 3 months (which certainly would be concerning), or if his readings move all over the place anyway but there's no upward trend.