That 100% sounds like an issue, and I agree that it would be bad form for Plarium to not honor this. Their Raid Digest back on the 1st of October (https://plarium.com/forum/en/raid-shadow-legends/843_news/20921_raid-digest--01-10-21/) specifically said the below. I would reach out to them if I were you
The Special Ninja Program is coming to an end!
Even the top teams for the Doom Tower include Ninja, a free Legendary Champion based on the famous streamer Richard Blevins. The last day to obtain this character for your account is October 15th. But since you need to log in for 7 days to get the Champion, you’ll have to start playing RAID on October 7th, at the latest. So it might be reasonable to invite your friends to Raid till then if you want them to have this remarkable Champion in their Collection. All players who join the game after the Ninja program ends will get an Epic Champion Shaman instead, the regular Daily log-in program champion.