I'm presuming that these worms folks are seeing in, and coming out of, the meat are migrating stages of Stephanurus dentatus, the swine kidney worm. I have not seen a case of Stephanurus infection since about 1980... but I've not worked on many feral swine, or even pigs raised in a dirt lot in that time... mostly conventional swine on concrete from conception to slaughter, which won't have exposure.
It takes 9-16 months from ingestion of eggs(or earthworms which have ingested the eggs) containing the infective larvae, until there are adults present in the kidneys, laying eggs. So... yes, the worms will be present during winter months.
Some of those larvae 'get lost' in their migration from gut->liver->kidney, and instead of making their way to the kidneys, they can go anywhere, and an animal infected with large numbers may have significant damage to muscle tissues - particularly the loins/tenderloins.