Before the Internet, when I ran my own small business, I took a seminar that taught me about using the priority matrix. That was useful, but the second part was even more useful and I'm struggling to remember how to implement it. It had you put your tasks on a grid, using rows and columns, running from Q1 to Q4 at the bottom and far right. You then compared each task to every other task and assigned it a number as to which task you felt was more important. The grid is easy enough to set up, but I'm having trouble remembering the number system and how to rate the tasks. Does this sound familiar to anyone? I know I kept the paperwork from this seminar, but after 20 years, it might be almost impossible to locate. (It's possible it didn't start with the priority matrix and was just a different way of prioritizing tasks.) Either way, at the end, you had this nice list of prioritized tasks, even if there were 50 of them. I'm looking everywhere for how to do this. If it had a name, I don't remember which makes it hard to search for.
Not sure if this is exactly what you're asking about, and pardon my shameless plug, but at work (we make Priority Matrix), we use the icon system heavily, with a preference for levels 1, 3 and 9. The reason is that we want to force ourselves to think whether something is a must-have (9), should-have (3) or nice-to-have (1). We could pick any arbitrary numbers, but having order of magnitude differences makes it harder to fudge a rough middle-ground priority that's really hard to compare later on.
Anyway, with this technique, the system still lets you sort by creation date, timestamp, completion, and other dimensions, without losing track of the actual micro-level priority that was agreed upon.
This post on Prioritization Matrix seems to be what you are referring to.
They number things from 1 to 5 as follows:
The approach you are writing about is called Pairwise comparison.
I'm having trouble remembering the number system and how to rate the tasks
There are many ways to rank the tasks. The simplest would be to just use 0-0.5-1 rank (lose-tie-win). A more complex way would be to create a list of comparison criteria, assign them weight and then make a weighted comparison against each criterion. You can find an example matrix for this approach here.
You may want to take into account that effort to make a pairwise comparison will grow as n2, where n is the number of tasks.