It doesn't matter:
Prior to UFC 182: January 3, 2015 - Jon's testosterone/epitestosterone (T/E) ratio was considered by some experts to be alarmingly low. Word of the “hiding under the cage” incident spreads.
Fail 1 : January 6, 2015 - Coke
Fail 2: July 8, 2016 - clomiphene and letrozole (1-year suspension but noted that may have been contamination)
Fail 3: August 22, 2017 - Turinabol (15-month suspension)
Fail 4: December 23, 2018 - Turinabol long term metabolite M3. (No punishment because USADA decided it was from 2017 use. Can't punish for same violation twice.)
One study estimated the detection window of M3 as 40–50 days: Detection and mass spectrometric characterization of novellong-term dehydrochloromethyltestosterone metabolites in human urine - Journal of Steroid Biochemistry and Molecular Biology
It’s extremely likely he was using Turinabol in October 2018.
"But he's not on it anymore" - Sherdog
Well even IF he stopped:
Muscle fibres have multiple nuclei, and the number of nuclei increases when muscle mass increases using steroids. When you stop using and working out they get small again but the number of nuclei remains the same.
When mice were briefly treated with steroids the muscle mass and number of nuclei increased. The drug was withdrawn for 3 months and the muscle mass returned to normal, but the excess cell nuclei persisted. When the muscles were subjected to overload they grew by 30% over 6 days while controls grew insignificantly.
They found that three months after the drug was withdrawn, their muscles grew by 30% after six days of exercise. A control group of mice saw growth of just 6% in the same time period.
