Buyers or lessees of collateral for value will defeat unperfected security interests attached to the collateral bought or leased, whether the security interests are granted by the seller or lessor themselves, or by another1.
Knowledge is irrelevant to this extinguishment rule. Even a buyer or lessee who knows about an unperfected security interest can give value and buy or take a lease of collateral subject to that unperfected security interest and extinguish the security interest.
This extinguishment rule shows the importance of promptly perfecting security interests. Otherwise, secured parties are at significant risk of having their unperfected security interests extinguished by a mere sale or lease for value
Notes:
1 PPSA section 43 (link)