Researching the reporting marks you listed reveals:
CEFX=CIT Group, an investment firm that leases freight cars as part of their portfolio. These cars are most likely assigned to a shipper as long as they are needed. Once the need is gone they move on to the next customer, possibly receiving new reporting marks. These cars could appear anywhere.
GLFX=Gulf Power Co. These don’t seem like cars found in northeast Ohio.
GGPX=GATX, a lessor of thousands of freight cars of all types. There may be a number of complete trains of these cars in service all over North America, including northeastern Ohio.
KPLX=Koppel Inc. Koppel is affiliated with Western Resources of Kansas, and these cars most likely feed the power plants of that state/region.
PGNX=Carolina Power & Light. The name says it all. Not likely to be found serving a power plant in Ohio.
You didn’t mention era but, the expansion and contraction of the coal industry, quite often makes these cars surplus. The owners try to find lessors but many wind up in storage. Some fairly young cars have gone to scrap, as the market shrinks.
Just to add a bit, an “X” at the end of the reporting marks means the car is privately owned - i.e., not owned by a railroad. With power companies, they often lease cars from a car leasing company so the cars are only used for hauling coal for their power plant(s), and apply a reporting mark indicating their control of the car.
I bought unfinished cars and painted one end blue for the rotary coupler end. I named my power plant Cumberland Power and Light. I used a lettering stencil to make a series of car numbers on a sheet of white copy paper and CPLX. I copied them on the laser printer at work as I didn’t want the numbers to run when put on the cars if I used an ink jet printer. By cutting out the CPLX and the car number as a square I positioned each one on the car and soaked it with one of the thin liquid glues to adhere it. Still running and none have come off after over 20 years
They may not be anywhere near the Carolinas if leased to another power plant.
Power plants that are in the same corporate structure may use the various train sets interchangabley.
Also power plants intentionally “mix” coal to balance cost and emissions requirements. They might mix eastern or Colorado coal with Powder River coal to get a certain emissions level. One of the biggest customers for Powder River Coal was Georgia Power.