It was likely produced in 1988 for the 1989 model year. Tons of bikes are sold for the Christmas season, so a 1989 Expert (as yours is) could easily be produced in a run done in 1988. 1989 was the only year Centurion offered black, the only year they offered Suntour GPX as a group, a change from the Shimano 105 they offered the year before. Suntour, previously the industry standard in friction shifting, was late to the indexed game and it cost them. It would be cool to have had a couple more years for Suntour to compete with Shimano on the indexing product, but it didn't happen.

For 1989, Centurion reported to the cycling press that they had "tweaked" the geometry of the Ironman, but then didn't seem to get those figures to the press. As a result, it was speculated on, but never proven. Test riders hated the rock-hard Panaracer Technova II tires (700x18) that any geometry improvements were overshadowed by the absolute dislike for the tires. In fact, the tires caused the CTL-370 wheels to have to be trued more regularly than most. Once the magazine testers went to 23's and Loctite, the wheels stayed in true.

Those who own/have owned several model don't generally notice a difference, especially among non-black Ironman models. However, some who have owned both a black '89 and other Ironman models, including '89 Masters, feel the black frame is a bit twitchy compared to the others. This could be purely psychological, of course. Every bike has a different ride, and if you tell me one is twitchy, I may convince myself of that. One noticeable difference for the '89 Expert is the use of 52/42 chainrings, while all other models came with 53/39. The GPX calipers were hidden-spring and very pretty, the shifters light and precise. Some didn't like the painted crank arms and hubs, but I saw one whose owner had stripped and polished, and it looked pretty ace.

Thirdgenbird has a very nice '89 Expert, and I've had a couple. Excellent bike, glad you've got it, and welcome to the nuthouse.