these are probably dorco st-100.
I just bought a pack of these last week out of curiosity and I'm convinced these are Dorcos. Sharp? Yeah, but harsh! Tore my skin up. Wouldn't dare use a blade twice. $.20/blade? I'll pass.
Check the packaging. If they are marked "Made in Korea" they are almost certainly Dorcos, and I agree, these blades are not sharp enough -- they tug painfully.
If they're marked "Made in Vietnam" they are not Dorcos. The Vietnamese blades are much sharper than Dorcos.