Thanks to both replyers. It does look like it's just a school bus and is just not advertised. There's other Stagecoach college services to Grimsby Boothby97, The College Flyer from Barton and the FC1 from Alford/Mablethorpe.
There's another bus I'm not sure exists, Stagecoach's 21 from South Killingholme to Ross House in the docks one way only in the morning according to the council's 2009 map seen at Cleethorpes Pier and Grimsby Hospital. It was listed on a 2014 timetable still in place on Dudley Street but isn't on Traveline either.
According to Humber Transport blog the re-numbering before Simplibus branding came out a 9V is/was listed on VOSA, the blog also pointed out the registration for the 20 incorrectly states Riby Square as it's end point.
VOSA don't always get there details correct. For a short period the 9V was listed on Traveline as (what is now the 10) in one direction only, with 10 being listed as services in the other direction. Obviously this never went ahead and became the 10. The 'V' would have stood for Victoria Street.
The CF is a public service, but FC1 is wrongly listed. First of all, Stagecoach no longer run such as service. FC1 started September 2013, operated by Stagecoach, and then was cancelled at the end of the 2013/2014 college year. Coopers tours now run the extra college services for Franklin College (except the 5C/51C) which run from/to Healing and Alford. The Alford bus also no longer runs via Humberston Tesco and Weelsby Road, which again is incorrect!
The 21 I believe is long gone, I recall that the timetable on Dudley Street (stop at junction with Bargate) did make reference to it back in the summer, before the renumbering.
The 8C I'd regard as a public service, as I've used it a couple of times (I use a Megarider as I'm a student). But when I used it last week, some general members of the public actually boarded and paid the £1.50 flat fare to travel! It has been registered on VOSA (though so has the 104/108/CF) but is not shown on Traveline (same as the 108).