The other thread was started 5 years ago and was inconclusive. It seems reasonable to me that enough time has passed to seek answers elsewhere and start a thread here (to be clear I don't make the forum's rules).
Most importantly, we should get to the bottom of this mystery!
The previous reasoning given for why Nathaniel Lock was not the maker of your porringer:
...the key in his mark is too close to the LO not to be seen on your mark and the symbol below the letters is not as much like a cross as in your picture...
Contrary to this, I believe the mark comparison above shows the mark used by Nathaniel Lock in 1713 had sufficient space between the key and the letters that it is OK for the key not to be seen on your piece.
I still vote for Nathaniel Lock.