If we have previously filed jointly, does it matter if the social security numbers are flipped?I.e. my husbands SS number was 1st the last 4 years but mine was this year

Although it does not matter, it could cause slight delays with processing your return if you are not consistent with the method used. 

IF you haven't prepared-filed yet...don't do it.

I've been told the IRS frowns on switching and can delay processing.....but beyond that, the software gets major mixed up as to who is who...relative to last year...and labels forms, like a W-2 for one spouse, as belonging the other ...and all other kinds of complications...possibly transferring improperly to state forms tooo.

There really is no good reason to switch ...even if the first person listed no longer has income..