the the SP lock for two years was never executed

No, the SP lock for two years was there till authumn 2016, then changed for 3 month.
But the proposed compulsary convertion from SBD was never executed indeed.
Yes, the idea was that 1 SBD should always be treated as 1 USD, however this "1 USD" would be locked for two years in case of high debt ratio.
My guess is that if that system would be implemented we would never witness SBD price as low as 65 cents, because people who want to power up would have intensity to buy SBD below 1 USD and convert it to SP.
However, the compulsory convertion wasn't actually in WP, it was just a proposal from Dan Larimer, here is the link
https://steemit.com/steem/@dantheman/steem-dollar-stability-enhancements