Thanks for chiming in Gerald.
The FAQ at
http://distro.ibiblio.org/tinycorelinux/faq.html#bootcodes explains that the
base boot flag disable extensions at bootitme. It might be semantics, but the name of this forum is also Tiny Core
Base Q&A. I am also running without X extensions, thus I expected ALT-FN for changing VTs, which as I said work as expected with chvt from the CLI. And anyone running X and using CTRL ALT Fn would be in my same position, needing to ALT-Fn to change to another VT (with ALT F7 probably bringing him/her back to X).
I still think the issue, being related to a bootcode is independent of the the two methods to extend the base system defined as the kernel + and (some) initrd in the FAQ. Reading further, multivt just provides the suitable inittab that bb will use at boot time, and will do the same on both Core and dCore initrds.
I might be wrong and people using
initrd=core.gz
do get a different behaviour/inittab than the one I described, but the doc says different and that is the reason why I am asking.
Cheers,
LDS