The point is that which names were in use by the Sassanids for those lands. I have read several middle persian texts and the Sassanids had no doubt that those lands where rightfully theirs. Besides, you never see the popular maps of the Roman empire without Egypt, Syria and Armenia, although their control was intermittent in those areas.
The point is, when you look at the Roman Empire you think of "us" and when you talk about the Persian Empire it is always "them". So you would favor minimal territories for your enemy.
No, what I am saying is that the Sassanids
never controlled most of the extreme eastern reaches of the empire.
It is known that th Romans controlled Egypt and Syria for the overwhelming majority of their existence (briefly losing control) and their direct control of Armenia, though intermittent, lasted centuries ( where for centuries, Armenia would swing between direct Persian and direct Roman/Byzantine control or be partitioned between the two).
The Sassanid Empire existed between 224-651 CE.
During that time:
a) All lands directly east of the Indus were controlled by:
i) Western Kshatraps ( till early 400s CE) for the region of Gujarat, southern Rajasthan and North-western Maharastra, followed by the Gupta Empire till late 480s CE, when these lands came under Hepthalite control. Following the ouster of the Hepthalites, these lands came under control of Harshavardhana ( his rule coincides with the last 30 years of the Sassanid Empire). These abovementioned entities were completely independent and at the very least, may've been friendly towards the Sassanids but most categorically not its vassals or subjugates.
ii) The land of Punjab came under the Gupta influence circa 280s CE and remained under Gupta control till the Hepthalite attacks, circa 480s CE. Following the Hepthalites, who maintained control between the Sutlej and Indus till 550s CE, the area came under Harshavardhana's influence. Again, the land east of Indus, at best, under any nominal Sassanid supervision between the defeat of the Kushans (circa 240s CE) and the rise of Chandragupta I of the Gupta Empire (circa 280 CE), following which, the land east of Indus (in the Punjab region) remains bereft of Sassanid influence.
iii) Sindh was under the control of the Kushans till 240s CE, following which, it comes under brief control of the Western Kshatrapas, following which, they are a part of the Gupta Empire till 480s CE. Directly after then, the Rai Dynasty rules from 490s CE onwards to 650s CE, with them being the vassals of Sassanids roughly from 570s CE to 630s CE.
My point is, the eastern frontier of that map, much like most of the frontiers of that map, depicts the Sassanid Empire at its maximum extent and is also anachronious: that map is a map of all lands ever controlled by Sassanids (and in the case of Gujarat, Rajasthan and eastern punjab, never), not all territorry within Sassanid Empire at any given time.
And lastly, i do not really consider any empiric map to be accurate if it potrays the maximal extent of an empire for a short period of its existence. Similarly, I do not consider Tibet to be a part of Tang Empire, even though they did rule Tibet briefly. I also do not consider Iraq to be a part of the Roman Empire, even though they conquered it a few times and ruled it briefly.