I bought a used Chrysler van a number of years ago.
On my first oil change the oil came out black. I started to monitor the oil very closely and found that it got black real quick after being changed. I kept changing it at regular intervals and as time has gone on, the oil now stays cleaner much longer between oil changes, in fact three quarters of the way since the last oil change and yesterday it was a dark gold on the dipstick.
I believe that the regular oil changes have cleaned up the engine over time.
That being said, you could go for an oil flush cleaning and then stick with the program after that and you should have no worries.
My 95 Maxima also purchased used has always had regular changes and even today at 240,000 Km I find it difficult to see the oil on the dipstick it's just so clean.