The route to Gillingham lasted longer, numbered N81 for a time (I think there was an N80 somewhere, perhaps an earlier part of the journey), being eventually withdrawn in 2002, whilst there was also an N60 (I think) to Watford.Interesting. I thought it might be a reluctance to name it after the two closest communities to the station - Pratt's Bottom and Badgers Mount!
Only ran on Friday and Saturday night, to get people home after a night out in town (much cheaper than a taxi). There may also have been some traffic in the reverse direction - those needing to get into town early. I guess they hoped it would make money. It stopped in quite a few places after Welling. Only lasted three years. Replacement now confined to London, where it serves more of Bexley Borough. More details at the dependable London Bus Route NX1 (londonbuses.co.uk)
Certainly on the N81, the journeys in the London-bound direction terminated in outer central London (e.g. New Cross), as by that point it was the start of the daytime service!