We can take the both a-3d,a-d,a+d,a+3d and a,a+d,a+2d,a+3d as the four consecutive numbers in an AP it actually depends on the type of question and they are namely

1 - If in the question we are only provided with the sum of the four consecutive numbers and we are neither provided with value of a nor with the value of d. In this case we take the four consecutive numbers as a-3d,a-d,a+d,a+3d this is because when we take the sum of four numbers it comes out to be

a-d+a-3d+a+d+a+3d = 4a .

And this 4a can be equated to the sum and hence we can we find the value of a and can proceed further.

2 - If in the question we are provided with the sum of the four consecutive numbers and we are also provided either with the value of a or with the value of d then we can take the four consecutive numbers as a,a+d,a+2d,a+3d this is because when we sum them up

a+a+d+a+2d+a+3d = 4a+6d .

And 4a+6d can be equated to the sum and we can find the unknown value it is either of a or d .

Thanks for reading