Years ago we had 2 International Harvester 375 disks, pretty good wheel disks for their time.

Front blades were worn badly, but rear blades were not bad.  At the time, I thought those blades were high, so we just replaced the front blades of those disks.

Neither one of those disks cut the same after that, two disks we had once loved became two disks we hated.  Since the front disks were again worn, we didn't want to replace the back disks, afraid we would again have the same problem in reverse.

Finally traded in the disks for the newer model CIH disks.

I would never change one gang of disks without changing all of the blades, no matter what the cost. 

And, at that time, used disks were surprisingly close to the price of old disks with new blades.  We decided we would figure cost of replaceing blades compared to trading the whole disk in the future, and never again re-bladed disks, as the economics of trading rather than repairing, considering the possibility of a bearing failure after reblading causing problems, never was close. 

(That last sentence was confusing, what I meant was it just wasn't worth it to reblade disks considering all the possibilities.)

Economics of repair change often, use this information only as a guideline.

Or, as my favorite saying of Gifford Knapp says:  "Food for thought".  (What a wise gentleman!)