Just turned on my Xbox and had an achievement pop. [HSC: GEEP GEEP!] - Operate the GP38-2 for 10 miles. Didn't know this could happen, but I'll take it. Not sure if there are any others that can be achieved without DLC, but I doubt it.
Other examples like that are Sherman Hill SD40-2 Tracks using CSX Version Sand Patch CSX AC4400CW counts for Cane Creek version HRR DB BR 422 Wuppertal Commuter SKA DB BR 442 Talented Riesa-Dresden 146.2 counts towards Main Spessart Bahn 146.2 Making Tracks Expansion Pack CSX-S SD40 counts towards Clinchfield SD40
There are quite a lot of other examples. This one here unlocked for me yesterday, too. And it's an achievement completionists nightmare. Thanks to that lazy programming, I've "started" many DLC's I don't even own.
The first one of these I came across was for driving the class 47 a certain distance on WSR. I unlocked it with the 47 on NTP before I bought WSR and that was back on 2020
That is worrying as I believe if you complete 1 achievements you are no longer entitled for a refund... That's why I still have Sherman Hill...
I've had plenty games I got refunds on where I had a significant number of the achievements already, MS are pretty chill about them. The game I had the most playtime on was one where a new DLC basically rendered it unplayable unless you bought it, as it replaced all the vendors with ones who only accepted DLC currency, and swapped out the loot tables so you needed the dlc to equip anything that dropped, even in the original story, making it impossible to even progress on a newly created character, and which I got refunded a year after buying it. MS gave me a full refund on it after ten minutes on the phone. Most games have some kind of achievement which pops during the tutorial, so before you will get to any game breaking bugs and the like, so it'd be ludicrously unworkable to have a policy based on them being unlocked.
That's odd, SMH has been the only DLC they didn't refund me, and incidentally was the only one I got an achievement before trying to refund. I guess correlation =/= causation