There was a factory cleanout from Newport in 2009 where a big Ruger dealer near me got a bunch of NOS -Sixes but they all came in cardboard boxes with shippers that had modern barcoded end labels. Some of them had incorrect catalog numbers.
I haven't heard of anything like that since, although as contender said, Ruger does sometimes put an old gun on GunBroker in whatever container they have and I think a few of those have been -Six series DA's in plastic cases. But they would at least put a reprint manual and a padlock in the case.
A new condition 9mm Speed Six might sell for $1K or more these days, so if you paid less than that, you did well. There are a lot more 2.75" guns than 4" guns, so if a 4", add some $$ to the value.