Yes, I'm not entirely sure how anyone is supposed to do Newark/Retford during the daytime (there's one northbound service at 0712 and that's your lot, whilst there's an excellent 3 southbound services before 0811 ... and then nothing until 2200), which is quite bizarre. I suppose you could go via Lincoln, but the connections mean the journey is 1hr50 going north and 1hr30 going south, so it'd be quicker to get the bus (indeed, it'd probably be quicker on a bicycle). Oh, and it's not a permitted route, so it's more expensive.
Grantham/Newark isn't exactly brilliant either - northbound it's 2-hourly for most of the day but then has a weird gap from 1554 to 1917 because one of the Lincolns doesn't stop at Grantham (is that an error?), whilst coming south there is a 3-hour gap followed by a 3hr30 gap (there's only one train between the 1545 and the 2215).