I usually leave about 20 cents of headroom before I drill any holes. In theory the drilling of nodal holes should not effect the pitch of the bar at all!! BUT... that is only if you consider the perfect theory that the hole is perfectly on the node and aligned along the node. Also assuming a hole of zero diameter. Given that even in the most perfect scenario the likelihood is that the angled hole will not align right on, and the hole diameter means that there will at least be SOME material removed inside the exact nodal point.... well then you need to leave a tiny bit of headroom to allow for the potential effect - even if it is very small.