So by flying a longer route, it becomes impossible to make a level restriction?
I'm getting very scared by some of the responses here.
I wasn't talking about distance vs height.
If the clearance was fly to XYZ, descend to FL210 by XYZ" and subsequently you get vectored away from XYZ (even if it is 10 degrees), then you are no longer going to XYZ and as a result are technically unable to make the vertical part of the clearance because you will be
ABEAM XYZ not
OVER it. Ie the clearance to be FL 210 by XYZ is only possible if you actually go to XYZ. so the clearance needs to be reissued eg "desc to fl210. be lvl
abm XYZ"