The first way to work around bubbles is like an insurance policy - Usually the ingots have some porosity on one side, and you keep track of this side as you go from round to square, then make that side the back of the blade. This way they are far from the cutting edge and supported by more metal around them. I've seen old swords at auction with small seams on or near the back that are certainly the residue of ingot bubbles.
The other thing to do is to watch for the subsurface porosity to show up during the round-to-square forging and file/grind them out as needed. Any dips in the surface at this point in the process will be long gone by the time you get to the shape of a blade blank.
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