Or is that other data gone forever.

Is there any disadvantage or advantage to deinterlacing?
I see many players can now deinterlace real time as they play video.
Digital TV I think also can deinterlace realtime or do not need deinterlacing.

movie player totem, vlc, smplayer do that.

Does WMP deinterlace real time?

Does this really only matter to some older TV or older software?

I think kdenlive / MLT uses Yadif for any deinterlacing.

When you say 'Force Progressive' is that in the render dialogue or clip properties as I think purpose differs.

Personally I leave interlaced and let the playback device do it, but choose method where available.

Alternatively Avisynth + QTGMC is a great script for 'high quality' deinterlacing.

If you want to use linux tools, Avidemux also has a nice set of deinterlacers, many are ports from Avisynth.

force progressive is in the render dialog. This make it a 480p type video, so it is not interlaced.