Your question is confusing but I'll try to answer what I think you're asking. Under California law, a DUI can be charged as a felony if the defendant had three DUI convictions within 10 years of the new offense. The fact that the new DUI, without priors, would be a misdemeanor is irrelevant. Prior convictions can elevate a misdemeanor to a felony.
When the DUI "tail" increased from 7 to 10 years, there were constitutional challenges brought on behalf of people who got new DUIs who were charged with priors more than 7 but less than 10 years old; the seven year "tail" had expired and then was revived by a change in the law. The courts have upheld the application of the longer tail, reasoning that it is the law at the time of the new offense that is controlling, and that the defendant knew (or more likely should have know) of the change in the law and been aware that there would be higher penalties if he had a DUI within the past 10 years.
Hope this helps.