Thanks for bringing that up, YCNZ!
The official circulation figures are here:
https://www.ecb.europa.eu/stats/policy_ ... ex.en.html
It's simply
outlandishly incorrect that 12.8% of fivers and 9.3% of tenners
in circulation ⁽¹⁾ are from the 1st series.
If I'm not wrong, these figures are not statistical but derived from the totals of
emmited minus redeemed. That being the case, all banknotes that are
kept, forgotten or lost — without ever reaching a central bank — will be included in the number of those computed by the ECB as "
in circulation".
Just like a lot of pre-euro currency banknotes were never exchanged to euros, there must be a lot of 1st series euro banknotes that will never be returned to central banks. (For example, pesetas equivalent to 1 575 million euros, which amounts to more than 3% of all pesetas in circulation in December 2001, were never exchanged until the end of the exchange calendar
19 years later. Source:
"El fin de la peseta", article in Economía Digital.)
In reality, as every EBTor can experience, 1st series banknotes are becoming really rare. Take for example the heavy-duty Frankfurt user
taucher's stats: out of their 50k+ fivers and tenners registered this year, 3 or less were from the 1st series). Or take the combined stats of all EBTors using EBTCheck: only 2.2% of all

to

banknotes entered this year were from the 1st series — and we all know that these are much more prevalent in higher denominations.
Portugal is one of the Euro Area countries where most 1st series banknotes, can still be found in circulation (in percentage of all banknotes circulating in the country). Still, #1 Portuguese EBTor
Leofer40's stats show that only 2.7% of his non-500-euros banknotes entered in 2022 were from the 1st series. My own stats show that only 0.4% of all fivers and tenners that I registered this year were from the 1st series (11 + 26 ∕ 3 124 + 5 852). [Also:

2.1%,

13.3%,

3.1%,

20.4%.]
_________________________
⁽¹⁾ May 2022 banknotes in circulation (1st series ∕ total), according to the ECB:

263 997 782 ∕ 2 060 275 313

270 800 535 ∕ 2 905 771 854