If you have them as separate drawing files, and you XREF them rather than INSERT them, when you change the source drawing they will all be automatically updated in every drawing they're used in, the next time it's opened.

If you get them from the master drawing using ADC, if you've altered the definition of a Block in the master drawing, right-click on its name in ADC and you can choose the "Insert and Redefine" option, which will update all Insertions of that Block in the current drawing.  You would need to do the same separately in every drawing you want that Block definition updated in.

I would just use the AutoCAD Design Center [ADC command, or Ctrl+2] to bring Blocks out of the master drawing.  That spares you the need to have separate .dwg files for each one, and to go through the procedure of Wblocking them all out of that drawing.  You can have ADC auto-retract over to the edge, and when you want another Block out of the same source drawing, just hover over that edge thingie and it will pop out again.

I have tested John's procedure because I wanted to be sure that the file created didn't include the block itself so it could lead to the impossibility of inserting that same block in an other drawing and it's OK because the new file created includes only the entities of the block and not the constituted block.

In explorating that particular file I found that there was no unities on that file unlike all my files.

Are there also others problems to do this procedure with already constituted blocks ( that is really interresting anyway ) ?