Well, this is not quite true...
1st. The only definite distinction between D.V and D.Va is the aileron controls, (brackets can be seen on uprated D.V-s even D.III-s).
2nd. The serial number alone denotes that the machine is a D.Va of the first production batch (5165-5426/17)
3rd. Yes, there were some further reinforcements in Albatros D.Va wings, but in the OAW built machines (that had brackets BTW)
and has nothing to do with the lack of brackets in some planes (of the first batch from my brief inquiry) .
Here is D.5390/17 (first batch) showing no brackets:
D.5409/17 (first batch) no brackets:
D.5629/17 (second batch) showing brackets:
D.5815/17 (second batch) showing brackets:
D.7098/17 (third batch) showing brackets:
D.7327/17 (third batch) showing brackets: