It's probably worth noting that Appley Bridge has 2tph. I have always thought it strange that Gathurst has just 1tph while Appley Bridge has 2, and downright crazy that Meols Cop only has 1. However, if the more frequent service is a cause of the higher official passenger counts, or a consequence of them, who can say.
Concessionary passes, season tickets and splitting CDRs will have an effect, certainly, but Blackrod appears to be a particularly extreme example of this. There are very few stations with an off-peak hourly frequency of just 1 train an hour which top half a million passengers a year in the official figures. The only others I know of are Stroud (large catchment, many direct London trains?), Hedge End (??), Downham Market (??), Liss (??), Hartlepool (bonus from Grand Central) and Knutsford (largeish, wealthy town - seriously underserved by both bus and train).
If the official figures were to be believed, Blackrod would see higher annual patronage than:
-Stourbridge Town
-Westbury
-Earlestown
-Penzance
-Dunblane
-Wrexham General
-Port Glasgow
-Chorleywood
-Moreton (Merseyside)
-Wakefield Kirkgate
-Aston
-Berwick-upon-Tweed
-Poulton-le-Fylde
-Oxenholme
-Altrincham
This seems... extremely unlikely, given the frequent service and prime location enjoyed by some of these stations. Blackrod lacks both.
Incidentally I am very surprised to see Berwick-upon-Tweed on the list. For a location with so many IC services but negligible on-rail interchange potential, demand is astonishingly low at 530k.