I have the Osbourne manuals, they show the seam sealer location, but not when it was applied.
I thought it was before the undercarriage paint so that it would be covered in undercarriage color, body color overspray and pinch weld blackout (to a limited extent).
What I have noticed is that the Osbourne Assembly Manuals have an assembly line sequence as part of the Ford drawing number. If you look at the lower right hand portion of most drawing, there is a drawing number consisting of the responsible engineering area, "E" = Electrical, "N" = Body, "W" = Weld & Sealant, "T" = Interior, Chassis and Engine Accessories are the exception. The next part of the drawing number is the year, a dash, then a four digit sequence number.
The item number on each page is also an assembly sequence number.
In the first few pages of many assembly manuals are instruction on how to do specific tasks. Applying sealant is there.
Spend some time reading each assembly manual. I recommend the paper version so you can make notes. For example, on many pages of my 66 Electrical manual are the locations of where the wiring harness label is located along with the color of the label, it's material and color of the printing.
Jim