this thread become somewhat complicated because you did not advise what you were trying to achieve in the first place.
Dos DISKCOPY is for use when copying the same format discs.
e.g. 3.5" DD to 3.5" DD (not 3.5"HD)
Dos COPY is for use when copying a file or files from/to different or same format media
Dos XCOPY is for use when different formats, directories or sub-directories are involved
As you have windows, just use its edit/copy facility and copy the entire floppy to a folder on the hard disk, then copy or transfer it wherever.
Be careful with old 3.5" HD floppys. If they have been formatted and used as DD you have to blank the 'extra' square hole with black tape. Because a new pc cannot read them as it sees them as HD.
I would not rely too much on a flash drive. Also if the data is important, make two backup copies.
Running old dos programs, is the next step.
Please advise back on progress.
Good Luck - Keep us posted.