We are a paying merchant member already that many of you know well and have been for over 5 years now. This is a "Rep" name we created. I assume the new site owner will work on this soon. We're considering creating a new brand. We do alot of printing, which helps us understand the need for certain substrate requirements and are thinking about extending our buying power and experience to other sign shops and direct to substrate printers around the country.
The reason you would want a 50x99 sheet is to allow for kerf when you sell a 4x8 sheet. Let's say you have a digital flatbed and a CNC cutter/router of some kind. A customer wants to buy eight 24"x24" aluminum real estate signs to fit into frames. When you cut them out on your CNC table, they will be slightly undersized by whatever diameter your router bit is. If you start with a slightly oversized sheet, say 50x99, you could space the signs out just a little and actually cut full sized 24x24" signs.
There are other reasons too, full bleed for example.
Now I realize 95% of the time the small amount one would lose to the router bit kerf is insignificant, but there are times when it matters.
If you don't regularly run smaller signs digitally cut (Zund, Esko, Gerber, Summa, etc) from larger sheets, then I see why this wouldn't cross your mind to need slightly oversized sheets. But if you do, and have trouble finding them, let us know!