I'm assuming this is a bug, or at least an unintentional oversight to the achievement system. The achievements "First Step", "Welcome, Stranger", and achievements granted for reaching a new tier, can't be gotten if the requirements for them were met before the patch. For example: I already hit tier 2 on my knight, however, since I reached tier 2 before the patch was implemented I don't have the achievement "Spiral Spelunker". Not to mention that I have no way of obtaining the achievement since I can't very well re-obtain tier 2 access. I'm not sure about the rest of the achievements. Now I hope you guys can grant these achievements to all the knights who already earned them and not make them have to re-obtain the achievements using different characters or something to that extent. Here's to keeping up the good work guys, Cheers.
Achievements are account bound, not Knight bound. You can earn "First Step" by by creating a new knight and making it to the Rescue Camp. "Welcome, Stranger" can be earned by going down to the entrance of Haven or just logging in and spawning there.
The Tier access achievements appear to currently have no fix other than using another knight on your account to earn it. That's not really a decent work-around though and should be fixed.
It appears that there's no issue with the other ones outside of disputes of when the system started "counting" your actions.