You see the problem is that due to powercreep WN8 has become an inaccurate tool to measure ones skill in the game since it is nowadays a lot easier to achieve a high average WN8-level which doesn't actually reflect the true skill of the player.
Whereas 4 years ago 1500 wn8 would have been considered above average it would today be considered bad/below average by most high-end players.
To remedy this and keep the rating viable as a way for top-clans to quickly measure the skill level of new recruits it was decided that new tanks/tank lines, including the Polish and Italian line, would be completly excluded from the WN8-rating altogether up until the point where there average global WN8-rating of all players would drop back down to the average rating of 4 years ago.
What this effectivly means is that these tanks are counted as "0-WN8"- tanks until that point so playing them would lower the WN8-rating across all players as they are played.
I hope I could clear up any confusions!
-Fabunil, purple poaster/representative of the wotlabs WN8-commitee