~ひょうしに(~拍子に)   => the moment [A], unintentionally / inadvertently caused something to happen N1
... も ... もない => Not...or not N3
Emphasize
ないものでもない/ないでもない => A is not completely impossible N1
Need/Requirements
ないでもない => is not entirely impossible N2
Emphasize negative meaning
なんともおもわない => think nothing of N3
Invariant
でもない => neither... nor... N2
Things do not match the prediction
がないでもない => is not entirely impossible N2
Explain
... ないものは ...ない => is not entirely impossible N3
Ability
なんとも~ない => can't ... like that N3
Evaluate
ものもV-ない => is not entirely impossible N4
Emphasize the negative meaning
~ ないともかぎらない => ~ It's unlikely... won't N1
Speculation
ないことはない/ないこともない => can do; is not impossible to ~ N3