So if you get the 121 set; you won't get the cold start o-ring that goes around the rotating cold start shaft,... and you'll end up with a 19mm seal you can't use.
...and if you order the DGK-126 you won't get the LDA o-ring (if you are doing a TD pump),.. and you'll get no shaft seal at all.
It all depends on what style pump you are working on. If it's a pump with fast idle but not an AAZ you will have everything except the fast idle on the LDA and the driveshaft seal
If you have a pump without fast idle you won't have the driveshaft seal and cold start seal
If it's an AAZ you are missing the fast idle on the LDA, the other lever thing that never moves on the LDA and the driveshaft seal.