I used the TEK you posted with the HDPE 2 milk jug. I have done 2 fresh extractions since the botched attempt both on 100g of fresh new bark. Each of these last attempts yeilded 300-500 mgs pure white crystal. I followed the TEK you posted exactly. I still have the milk jug containing the basified MHRB after having done 4 pulls all 75 ml, then combined in a pyrex tray and evaporated down to 50 ml total. when put in the freezer this yeilded 300ish mgs.
I normally freeze precipitate all my pulls separately so I can tell that by the fourth one that it's not worth the hassle of doing another. You could try one more pull of 75ml and see if anything drops out in the freezer that you might have missed.
I'm just looking through the tek to see what i've changed since I first started out.
step 2 - Lye, I don't weigh it but I know im getting around 100g due to the container I buy it in.
step 5 - I always let the lye, bark, water mix sit for 2 hours
step 6.5 - I don't heat the naptha unless it's just come out the freezer from a previous pull, if i want to do another pull right away I will put it in a warm water bath to bring it up to room temperature only, no warmer.
step 7 - I use 120ml naptha per pull. I don't roll the mix end over end, i give it a good slow shake and let it seperate a few times for about 15 mins before pulling.
step 10 - I don't leave a pull in the freezer overnight, I may have a very cold freezer but within 3 hours all the crystals have dropped out, so I am ready to use the naptha for another pull.
step 11 - I don't recrystallise. never felt the need as I get very nice white crystals.
I'm not sure that these changes will make much difference to you as I got nearly a gram the first time I tried and I followed that tek pretty closely, they just seem more convenient for me.
Maybe you were right about the bark not being the best, try a different source.
Peace