The problem - it's not 9 or larger than 9. So they are late! Very late! (see the spoiler below)
And of course you are right - there are infinite series which can be interpolated with the method above.
Where the problem came from? It came from...
I want to find out when the punk band Exploited will release a new album The sequence contains the differences in years between their existing 8 albums. They did not release any album since 2003, so it has been 9 years already.
Don't kill me with stones guys. It's a real life problem. A big problem LOL