There is no much to it. The title says it all. I check my sales today, and there was jurrasic kog'maw, but after play 4 games without checking it, the slot it was in refreshed, and it seemed as if I never opened it. I clicked it and battleborn kayle was there instead.
Copy pasta from the OCE boards -
Hey everyone,
Seeing some posts about sales changing in your Lunar Revel shop. The skins that are being replaced in your Lunar Revel Shop are scheduled to go on sale either in January or February. We don't want you to get a Lunar Revel sale only to see it in a regular sale over the next few days, so we have replaced those sales in the Lunar Revel Shop with different offers.
EDIT: For reference, here are the sales for February.
Hope this clears things up! ^-^
You guys think you had it bad? My 70% off dragon blade riven changed into 70% off samurai yi. Un fucking believeable.
http://imgur.com/a/HApuB ;-; rito pls
Blood moon Elise has been changed to Woad King Darius :( Damn and i wanted to buy that skin.... But i am not sure why this happend.
Thank goodness i bought Blood Moon 
immediately at 70% off instead of having it taken away and made me wait for 50% lol
Can somebody clear this out to me, I got the same thing, and read @Riot KateyKhaos' reply, but the weird thing with me is: It was Warring Kingdoms Trynd, which isn't supposed to go on sale in Jan or Feb because it is legacy. What happened?
I just had the same thing happen to me, i logged into league opened up all my discounts then i left the my computer. When i came back two of the discounts i opened had closed, like they had reset. I opened them again and they had changed!, tundra fizz had become atlantean fizz. And nighthunter rengar had become headhunter rengar!. This made me really upset as i was so happy that i had gotten those two and i was planning on buying them when i came back... God damnit :(.
My lunar revel shop had warring kingdoms tryndamere. and to my knowledge he isnt available al lthe time. so are you saying he will appear again in January at a discount?
I had Dragonblade Riven at one point, got out of game and reopened my sales, one was unlockable again. I unlocked and get BB Riven instead :(
Same thing happened to me. Mine changed from pool party leona to jade wukong
