There has never been a rule against adding vehicles that are test or experimental vehicles, even if they are current. There are many examples of them throughout the game in every nation (experimental/prototypical).
There are also plenty of examples of vehicles introduced to the game in / around the same time as they were in reality, such as the Leopard 2PL.
This was all previously explained and outlined here: https://warthunder.com/en/news/7289-development-reports-concerning-the-protection-of-post-war-combat-vehicles-en
The vehicle violates nothing at all. Sufficient information was available to model and introduce the vehicle, otherwise it simply would not have been introduced.
As always, our dev team are closely monitoring the efficiency of new vehicles when they are added and will make any necessary balance changes to any new vehciles (BRs etc) when the next balance patch comes unless there is an abnormality statistically that requires more urgent changes.
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