If it's that much thread and from an estate sale, I would think it is highly likely to be serger thread. While some quilters do use serger thread for quilting, I personally do not like it for that purpose because of the lint. Serger thread tends to have short fibers and therefore under a microscope looks fuzzy. That fuzz is what creates lint in your machine when you sew. I love my vintage Bernina, which was an extravagance when I purchased her almost 20 years ago, so I try to use only good quality thread in her.
The only reason to throw out that thread would be if it is dry rotted. I couldn't find the company by Googling.
Edit: Personally, for the difference in cost, I would go with something that carries less risk. For example, I found this cone thread on Amazon for a little over $3 a cone (shipping included):
https://www.amazon.com/IZO-Home-Good...dp/B06XDDRFCL/
and that was without looking. There are probably even better deals out there.
How much thread do you use in a year? If you use 4 cones, you are looking at a higher cost of about $4 per year if you buy new online. Not worth the risk of bad thread, in my opinion.