As someone who uses a dialect/accent of English that means I often pronounce these "silent" letters (e.g. I would pronounce the "h" in herb), I've often wondered if selection of "a" vs "an" is supposed to be accent specific.
I think so, yes; if you say "herb" with a non-silent 'h', you'd write "a herb".
By way of example, the name Herb is commonly pronounced with a non-silent H, so even in a dialect where "herb" is pronounced "erb", you'd write "A Herb picked up an herb.".
