There are 12 prizes on WOF. Currently shows 2 left. Odds of GP are 1 in 1.5M so 1,500,000 * 12 = 18 million tickets. Divide that by 60 and you get 300,000 rolls. Throw in the 4% extra tickets and you get 312,000, plus some skipped numbers, it looks like this game goes to Roll 320K or so.
On Average, there should be a Grand Prize every 25,000 or so rolls. Looking at the winning roll numbers, it appears 317823 was meant to be the last prize in the game.
0-26K - Claimed on 9867
26K-52K - Nothing
52K-78K - Claimed on 69272
78K-104K - Claimed on 88367
104K-191K - Nothing
130K-156K* Appears to be claimed on 163307
156K-182K - Appears to be claimed on 182893
182K -205K - Nothing - But should fill in the 216887 since the next prize was given away within just 5K rolls
205K-231K - Two Prizes - Claimed on 216887 & 221707
231K-257K - Claimed on 245741
258K-284K - Claimed on 277783
284K+ - Claimed on 317823
It appears the huge gaps for the 2 unclaimed prizes should be somewhere between 9867 and 69272, and the other between 88367 and 163307. Considering that a grand prize was within 5K rolls of another grand prize, it could literally be anywhere within those ranges. Since they appear to be older, not sure if these will ever be claimed.
Just my opinion though.