Let’s just set this straight and give some people some more inside info on what actually happened. This is more info then any casual collector is going to know and is a good reason to be a part of the forum.
Wizards of the coast starts production on Base set pokemon cards. They use the shadowless template and create a bunch of cards. Some of those cards are given a Thick 1st edition stamp. Some time goes by and they realize they miscaluculated the amount of Holo cards they needed stamped, so some shadowles holo sheet go back and get Thin 1st edition stamps applied. (We know some non holo cards got thin stamps applied to them, but I haven’t seen any factory rep explain why. Speculations have been made, but nothing confirmed).
The 1st edition cards are sold and sent out. Wizards still have a bunch of shadowless sheets which they cut up and sell as the intended ‘unlimited’ version. After this Wizards makes astetic and text correction to the templates and starts producting more cards. These new cards have shadows applied to them, and are sold off as unlimited cards. People notice the difference and start calling the old unlimited cards Shadowless.
There’s 6 more print runs done with these changes. The 8th and final print run includes the final corrections made (vulpix’s HP) as well as the copywrite date changed to 1999-2000. This print was done in a factory in the UK, and most of the packs have regular holo cards (2nd-7th print) put inside them.