It seems like the documentation to which you link also disagrees

I didn't say it invalid. I said it was useless. You never need to know whether an SV was allocated for an array element. You either need to know if an array element is defined or if it's beyond the end of the array. exists doesn't tell us either.

I decided to loop over the larger array (a1). In order to avoid a warning when checking the last element of a1 versus a non-existent element of the smaller array (a2), I decided to use exists.

In addition to doing that, it skips some warnings on elements before the last element.