Indeed, in fact I think the N29 was developed from a handful of very late/very early journeys on the 29.
Yes - from a 1976 'red book', the 29 has one bus which finished at Wood Green at 0209. Since the first journey of the day was 0451, I think this would have been a very late 'late shift' rather than a night shift.
Some routes were '24 hour' routes at that time - the 11, 177 (Sat night only) 185 and 220 each had one or two all-night duties. (The 177 was a particular scheduling oddity, remaining crew operated for quite a few years after the daytime service went - as then was - OMO.)
With the exception of the 11, these were all ex tram / trolleybus routes - and I think the late journeys on the 29 didn't come from its absorbing the 269 trolleybus replacement route.
Your subsequent post is spot on in respect of the pre-1970s route numbering. The N68, N81 and N82 were 1970s additions to the numbering sequence, all being variations of the 168, 181 and 182 routes (all tram replacement routes) - the night service on the N82 stayed several years after the 182 disappeared. (the 182 at one time ran something like Monday to Friday daytimes, and every night)
It's also notable that the south London night route network didn't budge from the tram route along Victoria Embankment to the logical traffic objectives of Trafalgar Square and Fleet Street for a long time.
And similarly, some routes did not extend to logical suburban termini - the N85 terminated (apart from one odd journey) at the site of the Downham Way change-pit (unstaffed at night) rather than extend through to Grove Park...
That having been said, LT tended to overlook the night routes - I've read somewhere that when the trolleybus to bus conversion took place between 1959-62, they noticed that the 'all night' services were still running on the revised timetables introduced to cope with the blackout conditions of the 1939-45 war...