I found this last year on my 4520. Some cylinders have, and some do not have, grease zerks(I suspect two different suppliers) . There is no hole, nor a boss that wasn't drilled out. I asked at dealer and got a "gee, I don't know" answer. At the time there was nothing in DTAC. I don't know if that has changed or not. After that, I wrote to JD via the support web site and got a "you need to contact your dealer" response. Someone else want to take a stab at it and let us know if the situation has changed?
I am slightly concerned as that area is subject to some of the harshest climate on the tractor. The position of the joint says to me it needs to be greased. I am planning that as soon as the warranty is out, I will disassemble the joint and add a zerk.