I know some of these multi-digit LED displays
I do not make simple multi-digit, but text LED displays (up to 24 rows by 200 columns).

Just to emphasize the points made in the previous posts, when I went from non-multiplexed Amber to multiplexed color I had to employ a Cygnal 50MHz 1 clock ( 50 times faster than plain vanilla) processor, just to keep up. Any multiplexing complicates a non-stationary display by at least an order of maginitude due the fact that LEDs do not have any persistence.

Erik