B1/B2 are usually issued for 10 years. But that doesn't mean that folks can come here and stay for 10 years. The maximum amount of time you can stay is 6 months. After 6 months your I-94 will expire and if you stay even a day after the I-94 expiration date, your presence is considered illegal even though your visa doesn't expire until 10 years later.

There is a formal application process to extend your I-94 expiration date. It is very difficult to get an approval because it'd show your intent to live the US permanently f0r 10 years.

Unless you originally came here on a J1 or F1 visa, your legal stay was for SIX months or less regardless of your visa validity date. I-94 expiration date comes first!