Well, IP address have nothing to do with this.
The whole concept of Blynk is that each device connects to Blynk with its own auth token. This allows the Blynk server to have an Always On connection with each device and to monitor that connection. The primary advantage of this in Legacy was that the user would be alerted if an individual device went offline. With your system, all three devices would need to go offline before the Blynk server was made aware of this, and could alert you.
In IoT, the other reason for individual auth tokens and device names is that it allows the Blynk.Air OTA system to be used.
In Legacy, there was no licencing cost attached to each device, so shared auth tokens wasn’t the Blynk staff were too worried about. They warned against it, because it’s not how the system was designed to be used, but that as all.
In Blynk IoT, licencing is based around devices and users, with limits set on each by the subscription plans. As far as I’m aware, Blynk don’t currently prevent or specifically look for another device connecting with the same auth token as one is already connected. But, think about how you would approach this if you were Blynk and you were looking to protect your revenue by preventing fraudulent use of multiple devices via auth token sharing. If it was me, I’d implement a system where if there was already an Always On connection with a specific auth token, and another connection was requested with the same auth token, I’d terminate the first connection and accept the second connection.
It may not work that way at the moment, but Blynk would be crazy not to implement this sort of checking in future.
So, my advice is to use Blynk as it is intended, and have unique auth tokens and device names for each device. This will create one tile for each device, and that may or may not suit your way of working. If it doesn’t then there are workarounds available.
I’d say that it’s better to do it that way than wake up one morning to find that only one of your devices is working, because Blynk have closed a loophole.
Just my opinion though!
Pete.