Not really something I should have known about per se, as in they’re commonly available like your Neo Genesis Clefairy example, but it still surprises me when we see cards from decades ago for the first time nowadays. The most recent example is the SNAP Magikarp, for which both the first sale AND first picture of a physical copy happened this year.
Some other recent examples (as in past two years) are: the DPt-P Cresselia and Darkrai (popped up in September 2020); the BW-P Pokémon Catcher, Emolga, and Metal Energy (popped up in June 2020); the original Japanese sample cards (popped up almost three weeks ago); etc.
And one that probably surprised me the most: the two Glossy Keiji Kinebuchi Ivy Pikachu versions, one from the October 1998 Gekkan CoroCoro lottery Comic that’s limited to 2k copies (popped up in September 2018) and one from a still unknown origin with shifted artwork (popped up in August 2021). This second one I’m still missing myself in my Pikachu collection, but I did find the first one recently. It still surprises me every time a new Pikachu is being discovered, especially those from pre-2000, considering how long the TCG already exist and everyone is collecting including myself.
Greetz,
Quuador