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Looks to be just old vs new part numbers for oem PS fluid. The formulas may vary minorly but the fluids should coexist peacefully. No one balks at using a gas station or box store fluid to refill if they spilled some. I would have even less concern using like GM and Delco products.
The ebay link I found for the old set here actually included the term "vintage" in the title. Couldn't hurt to flush the old fluid in the system if it is 20+ years old. There is a whole process for this with the PS system which comprises a few bottles of fresh, getting the car in the air, turning the wheels lock to lock numerous times to work the old fluid out and replace with fresh. So I also don't blame you for topping up and driving off.
