PB, the screwdriver tail can be retrofitted to earlier versions. Also the -88 looks identical to the -81/-82/-83 models. Some of Delta Air Lines MD-88s were delivered as -83s and then later upgraded to -88 standard. The only way to know what type it is, is to look at the paper work.
In the mid noughties American Airlines started to replace the old style tail cone with the screwdriver style.
https://www.flightglobal.com/news/ar...l-cone-218746/