Does anyone ever enter the GST number of the employer on the T777? I always wondered why that’s not a question on the T2200. How are we supposed to figure that out? In the past I have been applying for the rebate for everyone who has employment expenses but now I look at the industry and make a judgement as to whether the employer would be registered for GST. It’s a best guess at most but I don’t want to be holding back filing T1s while clients look for GST numbers. It’s a pain point and I am wondering what others do. Do you claim the rebate without the GST number?
Technically speaking the employer is supposed to certify your client’s GST370 application, so presumably they could complete their BN on the form at the same time they were signing it. 
I don’t claim any GST/HST rebate unless the client provides a signed GST370 along with their signed T2200.
I do what you do…most businesses are registered if sizeable and not in a proscribed industry. Can’t think of a small employer in recent memory that’s issued a T2200…onne of the few joys of working with mostly either seniors or self-employed (corporate or not) clients.