It's not a cure-all, but the good news is that many new products have the EDS embedded in them. Take a look at the default web page for a 1734-AENT, for example, and you will find a link to the EDS file that can be downloaded directly from the device. Many DeviceNet products, too, support the "upload EDS" wizard function because they contain a full Parameter object that RSNetworx can build an EDS from.
Anyhow, to the matter at hand with the PV+.
There are three drivers that can "see" a PV+ terminal on Ethernet; the RSLinx Classic "Ethernet Devices" driver and EtherNet/IP drivers, as well as the RSLinx Enterprise EtherNet/IP driver.
If it's one of the EtherNet/IP drivers and it shows a question mark, then we probably have an identity problem related to EDS registration.
I have also seen some instances where the user purposely or inadvertently deleted the Ethernet driver in the Target tab of the RSLinx Enterprise configuration. That meant that when the *.MER runtime file got loaded onto the PV+ terminal, it replaced the current RSLinx Enterprise configuration with one that lacked an Ethernet driver.
Even though Windows CE handles the IP address and basic TCP/IP functions for the PV+ terminal (which is why it will respond to PING), RSLinx Enterprie handles all the Rockwell-related services, including providing identity and services to other computers' RSLinx browsers. If the PV+ has no Ethernet driver, it will not respond to EtherNet/IP "List Identity" commands, which is what the PC's RSLinx Enterprise and Classic EtherNet/IP drivers use to discover Rockwell products on a network.
So; check which driver you're using to "see" the PV+, and check in the online Application Settings to see if there is an Ethernet driver configured.