I am trying to figure out the year of two Lincoln Idealarc TM-400 AC/DC stic welders.

code -8822-c   I am guessing that this one is a 72' from the serial number but it looks newer that the other one.  It has a gray face plate.
serial -487258

code -4444      If I am guessing correctly than this one would be a 77',but it appears older and has an orange face plate. 
serial -187713

I checked the lincoln website but did not see a way to reference.