Oh man I haven't traded actively in a while, but I will say that for pure math reasons I am
very in favour of banishing the 2:1 date rule to the nether realms where it belongs, especially with this new rarity granularity. Here's my reasoning.
The below is written out as explicitly as possible because hey, it's a children's website! But if you know what exponentials are, the amount of pets needed to trade up years increases exponentially as 2^x, and I firmly believe that this is silly considering the site's age.
Math time!
CS has been around for about 15 years now. Let's say that I have a rare from 2023, and want to trade for a rare from 2008. We know that these pets have the same rarity, and let's say that they also have the same demand (e.g. two rats).
So, let's look at what I have to do to get my desired 2008 rare. My first logical step is to trade for a 2022 rare. I scramble up a second 2023 rare, apply the 2:1 date rule, and trade for a 2022 rare.
Cool! I'm one step closer to my goal. So far, I have "input" two 2023 rares, and moved one year closer to my goal. Now, I want to get a 2021 rare. To do that, I need another 2022 rare, so I can apply the rule, and repeat. So I dig up two more 2023 rares, and trade for another 2022 rare. Then, I trade my two 2022 rares for a 2021 rare. So far, I have "input" four 2023 rares, and moved two years closer to my goal. Notice how that's already twice as many rares as I needed to move one year closer to my goal!
Let's do one more step, to see how bad it gets. I now want to trade for a 2020 rare. I have a 2021 rare, so to apply the 2:1 date rule I need one more. To do that, I need two more 2022 rares. To get those 2022 rares, I need another four 2023 rares. So I dig up another four 2023 rares, go through the trading process, and trade for my 2020 rare. So far, I have "input" eight 2023 rares, and moved three years closer to my goal. That's twice as many again...
Ok, let's figure out the pattern here. Every time I move up a year, I need to supply a second pet from the previous year. So the number of pets I need every time is multiplied by two. When I moved up one year, I needed 2 pets. When I moved up two years, I needed 2x2 = 2^2 = 4 pets. When I moved up three years, I needed 2x2x2 = 2^3 = 8 pets.
So how many pets will I need to move up the 14 steps between 2023 and 2008? Well, I'll need 2x2x2x2x2x 2x2x2x2x2x 2x2x2x2 = 2^14 = 16,384 2023 rares to trade for a 2008 rare!
In fact, you can work out that any x:y rule will eventually have this effect.
But it really really matters what the step size you apply the rule in is. Above, we had to multiply the number of pets needed by two every year! That made our number get very big very quickly. But what if we multiply the number of pets needed only every five years, like one of the suggested options? Well, then we only have 15/5 = 3 steps. Like we worked out above, after three steps the number of pets needed is eight. You'll have to decide for yourself whether that's reasonable.
TLDR: 2^14 is too large a number. There is absolutely no way that this ratio is representative of the real (or even the demand!) difference in rarity or value between a 2023 and a 2008 rare. I agree with Loelya's analysis that the new rarity categories are granular enough that there should be a much lower range of "real" rarity discrepancies within one category, but even if there weren't, a factor of sixteen thousand would still be
far too large a factor.
Therefore, this rule was always going to be outdated after a decade and a half, and we should take this opportunity to be rid of it while we're overhauling the economy anyways.Stay in math, kids. It helps in pet site economics.