So why do I have marauders with flails but no flails? Set the wayback machine for sometime in the late 90’s and WHFB 5th edition, it’s story time! Back when the army books were full of unit entries that didn’t necessarily have models available. Maybe they made them at one point but they were OOP. Maybe they never made them. But the rules were there if you wanted to use them. Army construction was also fun for chaos, where you picked a hero and built their retinue. Across both my undead and chaos armies, I made heroes to represent characters in a Rolemaster game we were playing. Gist of the campaign was that we had all sold our souls to the same demon, and were trying to get them back. One of the characters was an Arabian Nights type swashbuckling charmer dervish. GW made a named character for the bretonion line that would fit, but I needed some mounted marauders to back him up, and none were made at the time. Enter some DE Dark Riders.
A little clipping off speartips and replaceing them with flail heads later

Was it a bit wasteful? Ish. I always intended to get them new weapons, either stick some large mace heads, or axe blades, or something. Never got around to it. Until much later, when we actually got a plastic marauder kit. Which was not a good one. Although it did come with flail heads, which could be fitted to the old metals.

At one point in 8th WHFB my BIL at the time got me the core book and I was going to re-boot my chaos army. Picked up the army book, started cleaning up and painting some marauders. Never got them to the table before the world ended and AoS began. Where I returned to my undead roots.

And that was more info then you needed,