The original Nomad series had a derailleur drivetrain. The later series with Rohloff drivetrains were equipped with eccentric bottom brackets. It is easy enough to slide the eccentric to one side - or out -- to grease it for easy rotation during adjustment/to prevent galvanic corrosion, so a drain or grease port is not as critical.
The primary reason stated in early Thorn literature for the ports (when included) was for water drainage.
Older bicycles -- especially ones of British make, in my experience -- were often equipped with grease ports (often Zerk-style fittings, though sometimes cap ports) that allowed for greasing or oiling the bottom bracket in-situ. This required an "open"/unshielded/unsleeved bottom bracket so lube introduced through the port could reach the bearings. Modern bottom square-taper bottom brackets are now almost always sealed cartridge units with shielded bearings. In my experience, subsequent teardowns of the grease port BBs showed pretty uneven grease or oil distribution. The bearing nearest the port got the lion's share of lubrication, the other notsomuch.
Most water collecting in a bottom bracket enters from above in normal use (submersion, say when crossing a stream, is another matter!). Mindful of that, be sure to use grease to make a seal around the top of the seatpost. I also employ some tapered silicone rings that make a small "roof" over the top of the seat tube to prevent water entry. A section of innertube rolled over the split tightening kerf helps prevent water entry also.
Particularly on bikes with threadless headsets, it is also helpful to apply a small piece of electrical tape over the vent hole at the head tube/downtube junction to prevent water entering along the steerer from running down the downtube toward the BB, where it could collect and cause rust.
Best, Dan.
