A fern rootstock is commonly referred to as a rhizome and have never before heard anyone call them a bulb?
I have purchased fern rhizomes, but all have been freshly dug and shipped in moistened green moss. Have some on order now, Northern Maidenhair, that will be shipped in mid-November.(after they become dormant). Personally, I would prefer buying the small ferns in 4" pots from Growers Outlet at the same price($1.50 ea.). Have had 100% success with those. The ones I got from them in July is now in gallon pots and ready for planting.
Rb

that is typical for those bagged plants sold at lowe's.
they also print the planting instructions on the back or inside flap and everything is to be planted at "4 inches below soil level" and "zones 4-9". i have tried different packaged plants from there and some grow, some are dried up/dead. the real bulbs normally do fine for me but the rhizomes are "iffy". feel them through the plastic and move them around, checking for some (fleshy?) substance vs. dried-up remains.
you will have to wait longer on these to mature. even if there are 4 per bag, they probably will be small starts.

There are a few ferns that produces bulbils. One is on the leaf itself. But it is not realy hardy here and treated as a houseplant. (Mother fern) I doubt it is that.
The other is the common house fern which has several varieties. It produces pea size round bulbils.
I have bought some but made sure the pack was moist. And the ones I have bought were labeled. They were hardy garden ferns such as Maidenhair, Autumn fern and wood fern.
Also do not plant fern roots deeper than 1". Keep very moist with lots of compost the first year esp.

I HAD SOME WHEN I LIVED IN MO. THEY ARE JUST WONDERFUL... I'V HAD A HARD TIME FINDING THE BULBS SENCE ( THE OTHERS WAS GIVEN TO ME BY A FREIND) BUT, I KNOW WHERE THEY ARE NOW. SO I'LL GET ME SOME. THEY SPREAD VERY WELL TO. I JUST LOVED EM. THANKS FOR SHARING :-)
SHORTY