Liquid methadone- is the bottom of the bag stronger?

Sometimes when I take my dose it tastes more bitter and I can feel it more, other days, not so much. Not that I withdraw or anything though. Today the nurse mentioned to another nurse that one more person after me until the bag was full, so I know it was the bottom of the bag. Now it's been about 3 and a half hours, and I'm feeling sleepy and overall feel pretty good. I'm on 120mg and I've been going for a year and 8 months, and it probably took me 2-3 months to get stable, tbh I forget though. Anyways, is this even possible? I do know this has happened at least once or twice a week since I've been going. Maybe not every time while I had my week takehomes, but it happened often. Also, has anyone heard of losing all of your phases because of missing a day? I missed a day and had counseling that day, I missed my ride because I had overslept. Anyways they told me id go back to phase one for 30 days, but after that they decided not to give them back still. Aside from false positives (which one was deemed false by the doctor and the rest tested out fine), I haven't had positive drug screens nor have I used anything aside from psychedelics very minimally.