Grey Area:
If you are allowing your lockbacks to get that dirty I would not be counting on them for defensive purposes for the reasons you stated.
My EDC defensive knives are never dirty, let alone dirty enough to have them not lock open. Work knives daily, it isn't needed in a hurry, defensive knives [ any knife clipped to my pocket is a defensive knife ]need to be quick in the presentation and pristinely sharp, clean and with an oiled blade.
CODE 3: Only a matter of time if you carry them long enough, use them often enough, and engage, disengage the locking mechanism.
I'm not bashing linerlocks, I still have many in the fold that are customs, semis, and production folders from 50. to 450.00 in price. They are not longer carried for defensive purposes for reasons already stated.
On the spinewhak test, the palm of your hand would have sufficed, just make sure you keep the knife positioned in the hand so if and when it does release your fingers aren't in the way.
Linerlocks are the fastest for me to deploy, literally less than a second to open and defending
with them. Experience shows me the locks may fail at the wrong time for any number of reasons. It's not any different than presenting the gun and not having fire when you need it to.
I've done some testing and reviews at
www.folders-r-us on tactical folders of various quality. All have passed the stab tests admirably so far, spinewhacks were not performed but will now be incorporated into the reviews in the future.
I actually have been converted through this forum to test for the liners failure thusly as others have experienced it and had been testing their blades for some time in this manner. Many have failed and it remains a concern throughout the life of the lock whether it's used often and wears sooner or not used often and wears over a longer period of time.
I play with the blades I carry at least 50 times a day in opening hard and putting them away. It wears parts on them, the liners are prone to suffer sooner than others.
I still like the designs and makes from production and customs in this configuration, but they sit in the drawers, no not mine, but the wooden kind.
Brownie