Thanks for sharing your opinion. My opinion is that if I had done that, people would have wondered if they were missing 2a and 3a.
In hindsight, I'd probably say 2.1 and 3.1 would have been more intuitive than 2a and 3a. I think when you first see 2a and 3a, it feels like they should come before 2 and 3 - at least that was my intuition.
However, as soon as I read the order in the rules, it was clear and after that wasn't difficult to remember.
So I'd say it's not a huge issue and it's not like it's really obscure and difficult to remember, once you know how it works.
It's not like the new mats were numbered 20 and 30, and the order was supposed to be 2, 20, 3, 30 - that would have been confusing...