Here's why:
* GT Trim: The GT was a higher trim level than the base model, meaning fewer were produced.
* T-Tops: T-tops were a popular option, but not standard. This means fewer Fieros had them, compared to those without.
* Year: 1988 was the final year of the Fiero. While production numbers were up that year, many were not GT models and not all had the T-tops.
* Survival Rate: Many Fieros, including GTs, have been lost to time due to rust, accidents, and neglect. This reduces the number of surviving vehicles.
To find a truly precise measure of rarity would require extensive research into GM production records (which may not be publicly accessible in this level of detail) or a deep dive into Fiero enthusiast club databases. You would likely need to search databases and online classifieds, then manually compile numbers of available cars to get a general idea of what's currently "on the market" in a given condition range.
In short, while not *extremely* rare, finding a well-preserved 1988 Pontiac Fiero GT with T-tops in good condition is likely less common than finding a standard Fiero.