Ok, I've done that.
Now the firmware version is 74.30409.
And for this one, I can't find a patched firmware one on this site either
Now below are the steps I've taken in trying to proceed. These steps left me with some questions

.
So, here goes the lengthy post:
1) I wanted to get the new firmware from the Storio2. So I installed the SpiffyHack on an SD card, inserted it in the Storio2, but alas, nothing happened when I inserted the original cartridge that came with the device and went to the cartridge game. No menu was shown.
2) Then I found in the FAQ a way to extract the firmware from the .ugdx update file. I followed the guide and succeeded to get the 'bundle' and 'system' binaries. I could not get the last binary ('rootfs') since searching on the string '1F 8B 08 00 D8 B2 F3 50' resulted in zero hits.
3) Next I retrieved some modified firmwares that were close to my version (since I wanted to get to know what was changed to the firmware so maybe I would be able to do this myself). So I got the s2_uk_v74.30408_mod version and the s2_fr_v74.30321_mod version.
4) I extracted all the files (also the ones in the .bin file which seems to be only the 'system' part of the .ugdx file (so you don't need the 'bundle' & 'rootfs' ??)) and I compared them. Strangely enough, all files are identical to each other. Does this mean that the version and language do not really matter ? Where is the language choice then stored in the Storio2 ?
5) Next I compared all files from the s2_uk_v74.30408_mod .bin file with the 'system' files I retrieved from the ugdx file. And here only 2 differences occur: one in /bin/vtech/RunApp and another where the file only exists in the mod version: /bin/vtech/RunApp~
So, now I get to the main question: since apparently there are no differences in the firmware files between the different versions/languages of the latest firmwares, can I safely assume that I can use e.g. the s2_uk_v74.30408_mod version to flash my NL v74.30409 Storio2 ?
Thanks.