L1 to H1 Approved - COS or Not?

[dev2design]

I am currently in L1 and applied for H1 visa through premium processing(Cap exempt using old H1).Today USCIS status shows it as approved!!! But How do I know it is approved with COS or consular processing? Or it can be confirmed only when the attorney gets the I-797 with attached I-94? Is there a way attorneys to know it now itself by calling USCIS or so?

Since the I-797 mail may take 5-6 days or more because of holidays , can I work for L1 employer till attorneys receive I-797 with new I-94 and then join H1 employer since I am not sure it was approved with COS or not?

Thanks