That's funny as I had a shop with 82,500 5 star reviews and still have one with over 68,000 that does not show up in the top 100, how is your 280 review shop showing up in the top 100? Do you mean in a very specific niche or in your category? Or do you mean every shop on etsy, as both mean very different things.
You just answered your own question, as you say you didn't do it when uploading so now if you want to do it you will have to open each listing individually and insert any variations you want included. There is no way around that sadly. The bulk importer is famous for messing stuff up like this and in most cases one would have to go in anyway to make sure everything is in its right place and it carried all the info across. My advice would be to open up the listings and edit them by hand, 500 should not take you more than a day.
Most of these apps and tools to bulk upload dont work on Etsy and eBay because each section or type of products has a different page and a whole bunch of different options and variation so you are shit out of luck as far