never have heard of soft or hard frets. A wider fret surface may last longer but be harder to play and less accurate with intonation.

I have heard rumors that fret wire is made soft so you aren't replacing strings everytime you tune. It's probably a wash as far as cost of the first 7 frets or 25 sets of strings every six months. As it is I replace the strings every couple weeks.

A mandolin that old I'm surprised has nickel frets. many instruments from that age had brass frets with square profiles. Ofcourse that could be the cheaper instruments and the high quality instruments had a different fret entirely.

Don