It's hard to say actually, as that union tag was used from the 30s till the 90s. I'd be more likely to estimate 50s. And if my memory serves me correctly, the ugwa was not "registered" until about 1950.
[[SPOILER]] Plasterboard installed, cleanup and attic insulation tomorrow, plaster started by end of this week. Stairs Entry Closet Common Room Main Office and Photo Bathroom Hall and Deodorizing Chamber