H1B Stamping (Canada) - Offer letter query

[user1990]

Hi,

I am currently working in Canada on a work permit for employer A. I have an H1B approval notice valid from October 2021 for employer B in the US. I got an appointment for visa stamping next week (November 2021). 

I have a query regarding the offer letter. The current offer that I have - mentions a start date of August 2021. I do not have an updated offer letter and not sure if the employer can generate a new one on such short notice.

Is an offer letter mentioning future start date - a compulsory document? Should I reschedule my interview until I get the offer letter with future date? The problem is - next available visa appointment is in May 2022. 

Thanks!