Hi d0cwh0...
It mostly depends on what sell fabric you are using. I had the pleasure of taking a 1950's London Fog coat apart and there was nothing attached to the outer shell at all. However, the facing had an interlining attached to it all around, but not fused. A cut to bias loosely woven band was sewn aronud the shell. The same was actually sewn to the undercollar by means of a zigzagging topstith and to he back af the collarband by rows of stitches at 5mm distance. I suppose to raise the seams slightly. Mind you; at that time starch as well as "repellant" were used by drycleaners as a service...
Frankly, in your place I would just use a fusable for undercollar, facing and collarband and if the fabric is stable, leave it at that and sew a bias silesia or similar to the outer shell...
Cheers, Hendrick