I have original Microsoft floppies, unfortunately they appear unreadable. Were stored in protector, in a box, in a dark and dry place for the last 20 years. No dust, moisture or exposure to magnetic fields as much as I remember. They just seem to lost magnetic charge. Provided that's the only thing that happened to them, can I write disk images to them in attempt to restore it (at least for some time) or I'm better of just transferring labels to a brand new, good quality disks?
Provided that's the only thing that happened to them, can I write disk images to them in attempt to restore it
Yes. However, it's rare for floppies to just "loose magnetic charge", unless they have been stored somewhere where they were exposed to magnetic fields, or other unfavourable conditions that caused this to happen. Though the magnetization does get weaker over time.
What happens more often is that the surface of the floppy degrades (the metaloxide particles that store the magnetic charge get loose to some degree), and then you are
better of just transferring labels to a brand new, good quality disks
The only way to find out is to format the old disks, write all of their sectors, read them back, and see if that works without read errors.
If it does, in most cases the floppy should be fine for longer usage.
To make them functional again you need to do a low level format. The floppies looks like they for PC (MS-DOS). In there you could type
Format A: ...
but that is not a valid low level format and will not remedy your floppies. What you need is to use FHFORMAT utility (in MS-DOS). That will remagnetize and restore the surface index data ...
Just take in mind that for most 1.44 MByte floppies the safe data retention is only up to a 1 year.