depends on if you buy them tapered before they are spined or spined before they are tapered. If you buy spined after they are tapered they should be what you desire +/- 5lb spine. If you buy them as parallel (matched +/-5lb) and then have them tapered I have seen them very as much as 10lbs afterwards... Depends on spine range also. Light spines very moreso than the heavys.
ie. light spines tend to be effected more by tapering than do the heavier spines.
example: 45lb spine may lose as much as 5-7lb by a taper from 11/32- 5/16 at the nock, when an equal shaft of 75lb may only lose a pound or two at most subject to the same taper.
ain't wood fun!!
stump