Client letter for H1 visa requires project start date & End date

I have applied for H1 visa and it is in RFE status.If i submit client letter without project start date & end date will USCIS accepts it. Please let me know

and also how can i know what all documents requested by USCIS if the case is in RFE state

You need to find out from your employer what the RFE is for. Then you will know what details need to be submitted. As for client letter, it is better to have a dates mentioned.