Do solo night time and “towered” landings total separately toward the solo night requirements in FAR 61.129?
Night time does not need to include a landing at a controlled airport to count.  You just must have at least 10 solo night landings at a controlled tower, as well as 10 hours of solo night time, they don't have to happen together (though whatever time it takes you to get those landings counts toward the 10 hours too).

The pilot in your question would have 501 solo night hours and 10 towered landings.