A serial number beginning with 1R8 was unique to version 10.0 of the software. For later versions, this prefix changed; for example, Vegas Pro 12 typically used serial numbers starting with Boris FX Forum
If you are trying to find a legally purchased serial number for an old installation, there are several reliable methods: sony vegas 10.0 Sony Vegas Pro 10 Serial Number Starting 1r8
: These keys typically followed a 20-character alphanumeric format (e.g., 1R8-XXXX-XXXX-XXXX Authentication A serial number beginning with 1R8 was unique to version 10